General constraint information syntax in video coding

ABSTRACT

A method of processing video data comprises performing a bitstream conformance process that determines whether a bitstream that comprises an encoded representation of the video data conforms to a video coding standard, wherein the bitstream conformance process determines that the bitstream does not conform to the video coding standard when at least one of: a chroma-related constraint flag is equal to 0 and when there are no chroma components for pictures in the bitstream, or an inter prediction-related constraint flag is equal to 0 when all slices of the bitstream are I slices.

This application claims the benefit of U.S. Provisional PatentApplication 63/004,296, filed Apr. 2, 2020, the entire content of whichis incorporated by reference.

TECHNICAL FIELD

This disclosure relates to video encoding and video decoding.

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, tablet computers, e-book readers, digitalcameras, digital recording devices, digital media players, video gamingdevices, video game consoles, cellular or satellite radio telephones,so-called “smart phones,” video teleconferencing devices, videostreaming devices, and the like. Digital video devices implement videocoding techniques, such as those described in the standards defined byMPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced VideoCoding (AVC), ITU-T H.265/High Efficiency Video Coding (HEVC), andextensions of such standards. The video devices may transmit, receive,encode, decode, and/or store digital video information more efficientlyby implementing such video coding techniques.

Video coding techniques include spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (e.g., a video picture or a portion of a video picture) maybe partitioned into video blocks, which may also be referred to ascoding tree units (CTUs), coding units (CUs) and/or coding nodes. Videoblocks in an intra-coded (I) slice of a picture are encoded usingspatial prediction with respect to reference samples in neighboringblocks in the same picture. Video blocks in an inter-coded (P or B)slice of a picture may use spatial prediction with respect to referencesamples in neighboring blocks in the same picture or temporal predictionwith respect to reference samples in other reference pictures. Picturesmay be referred to as frames, and reference pictures may be referred toas reference frames.

SUMMARY

In general, this disclosure describes techniques for general constraintinformation syntax signaling for video coding. The techniques of thisdisclosure may be applied in the Versatile Video Coding (VVC) standardand other future video coding standards. As described herein, thisdisclosure describes techniques that may enable devices to correctlydetermine whether a video decoder is configured to decode a bitstream.Making this determination may potentially enable the video decoder todecode more bitstreams than if the determination was made incorrectly.

In one example, this disclosure describes a method of processing videodata, the method comprising: performing a bitstream conformance processthat determines whether a bitstream that comprises an encodedrepresentation of the video data conforms to a video coding standard,wherein the bitstream conformance process determines that the bitstreamdoes not conform to the video coding standard when at least one of: achroma-related constraint flag is equal to 0 and when there are nochroma components for pictures in the bitstream, or an interprediction-related constraint flag is equal to 0 when all slices of thebitstream are I slices.

In another example, this disclosure describes a device for processingvideo data, the device comprising: a memory to store a bitstream thatcomprises an encoded representation of the video data conforms to avideo coding standard; and one or more processors implemented incircuitry and coupled to the memory, the one or more processorsconfigured to perform a bitstream conformance process that determineswhether the bitstream conforms to a video coding standard, wherein thebitstream conformance process determines that the bitstream does notconform to the video coding standard when at least one of: achroma-related constraint flag is equal to 0 and when there are nochroma components for pictures in the bitstream, or an interprediction-related constraint flag is equal to 0 when all slices of thebitstream are I slices.

In another example, this disclosure describes a device for processingvideo data, the device comprising: means for storing a bitstream thatcomprises an encoded representation of the video data; and means forperforming a bitstream conformance process that determines whether thebitstream conforms to a video coding standard, wherein the bitstreamconformance process determines that the bitstream does not conform tothe video coding standard when at least one of: a chroma-relatedconstraint flag is equal to 0 and when there are no chroma componentsfor pictures in the bitstream, or an inter prediction-related constraintflag is equal to 0 when all slices of the bitstream are I slices.

In another example, this disclosure describes a computer-readablestorage medium having stored thereon instructions that, when executed,cause one or more processors to store a bitstream that comprises anencoded representation of the video data; and perform a bitstreamconformance process that determines whether the bitstream conforms to avideo coding standard, wherein the bitstream conformance processdetermines that the bitstream does not conform to the video codingstandard when at least one of: a chroma-related constraint flag is equalto 0 and when there are no chroma components for pictures in thebitstream, or an inter prediction-related constraint flag is equal to 0when all slices of the bitstream are I slices.

In another example, this disclosure describes a method of processingvideo data, the method comprising: performing a bitstream conformanceprocess that determines whether a bitstream that comprises an encodedrepresentation of the video data conforms to a video coding standard,wherein the bitstream conformance process is able to determine that thebitstream conforms to the video coding standard regardless of a value ofa first syntax element when a second syntax element indicates that onlyone slice is allowed per picture, the first syntax element indicatingwhether only one subpicture is allowed per subpicture.

In another example, this disclosure describes a method of processingvideo data, the method comprising: performing a bitstream conformanceprocess that determines whether a bitstream that comprises an encodedrepresentation of the video data conforms to a video coding standard,wherein the bitstream conformance process determines that the bitstreamdoes not conform to the video coding standard when a chroma-relatedconstraint flag is equal to 0 and when there are no chroma componentsfor pictures in the bitstream.

In another example, this disclosure describes a method of processingvideo data, the method comprising: performing a bitstream conformanceprocess that determines whether a bitstream that comprises an encodedrepresentation of the video data conforms to a video coding standard,wherein the bitstream conformance process determines that the bitstreamdoes not conform to the video coding standard when an interprediction-related constraint flag is equal to 0 when all slices of thebitstream are I slices.

In another example, this disclosure describes a method of processingvideo data, the method comprising: determining that a first syntaxelement is omitted from a bitstream and inferred to be equal to 1 basedon a second syntax element indicating there are no chroma components inthe bitstream and a third syntax element indicating that all slices ofthe bitstream are I slices, the first syntax element being one of: ano_qtbtt_dual_tree_intra_constraint_flag, a no_ccalf_constraint_flag, ano_joint_cbcr_constraint_flag, a no_cclm_constraint_flag ano_ref_wraparound_constraint_flag, a no_temporal_mvp_constraint_flag, ano_sbtmvp_constraint_flag, a no_amvr_constraint_flag, ano_bdof_constraint_flag, a no_dmvr_constraint_flag, ano_affine_motion_constraint_flag, a no_bcw_constraint_flag, ano_ciip_constraint_flag, a no_fpel_mmvd_constraint_flag, or ano_gpm_constraint_flag' performing a bitstream conformance process thatdetermines whether a bitstream that comprises an encoded representationof the video data conforms to a video coding standard based on the firstsyntax element.

In another example, this disclosure describes a method of processingvideo data, the method comprising: performing a bitstream conformanceprocess that determines whether a bitstream that comprises an encodedrepresentation of the video data conforms to a video coding standard,wherein the bitstream conformance process determines, based on a firstsyntax element in a sequence parameter set (SPS) indicating that acoding tool is enabled, that the bitstream does not conform to the videocoding standard when a second syntax element of the bitstream indicatesthat the first syntax element shall have a value indicating that thecoding tool is not enabled.

In another example, this disclosure describes a method of processingvideo data, the method comprising: performing a bitstream conformanceprocess that determines whether a bitstream that comprises an encodedrepresentation of the video data conforms to a video coding standard,wherein the bitstream conformance process determines that the bitstreamdoes not conform to the video coding standard based on a first syntaxelement having a particular value indicating a requirement of bitstreamconformance is applicable and based on the requirement of bitstreamconformance not being satisfied, wherein the requirement of bitstreamconformance specifies one of: a second syntax element specifies a videoparameter set (VPS) identifier of a sequence parameter set (SPS) shallbe equal to 0, the second syntax element shall be equal to 0 and a thirdsyntax element, plus 1, specifies that a maximum number of temporalsublayers that may be present in each coded layer video sequence (CLVS)shall be equal to 0, the third syntax element shall be equal to 0, or afourth syntax element shall specify that all layers in a coded videosequence (CVS) are independently coded without inter-layer prediction.

In another example, this disclosure describes a method of processingvideo data, the method comprising: performing a bitstream conformanceprocess that determines whether a bitstream that comprises an encodedrepresentation of the video data conforms to a video coding standard,wherein the bitstream conformance process determines that the bitstreamdoes not conform to the video coding standard based on a first syntaxelement having a particular value indicating a requirement of bitstreamconformance is applicable and based on the requirement of bitstreamconformance not being satisfied, wherein the requirement of bitstreamconformance specifies one of: there shall be no Network AbstractionLayer (NAL) unit in the bitstream with a NAL unit type equal to a VideoParameter Set (VPS) NAL unit type in an in-scope output layer set, orthere shall be no NAL unit in the bitstream with a picture header NALunit type in the in-scope output layer set.

In another example, this disclosure describes a device for processingvideo data, the device comprising one or more means for performing anysuch method. A computer-readable storage medium having stored thereoninstructions that, when executed, cause one or more processors toperform any such method.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system that may perform the techniques of this disclosure.

FIGS. 2A and 2B are conceptual diagrams illustrating an example quadtreebinary tree (QTBT) structure, and a corresponding coding tree unit(CTU).

FIG. 3 is a block diagram illustrating an example video encoder.

FIG. 4 is a block diagram illustrating an example video decoder.

FIG. 5 is a flowchart illustrating an example method for encoding acurrent block.

FIG. 6 is a flowchart illustrating an example method for decoding acurrent block of video data.

FIG. 7 is a flowchart illustrating an example process in accordance withone or more techniques of this disclosure.

DETAILED DESCRIPTION

As described herein, VVC specifies that a video encoder may include aset of general constraint flags in a bitstream. The general constraintflags may include chroma-related constraint flags and interprediction-related constraint flags. The constraint flags may specifywhich coding tools are used in the bitstream. However, thechroma-related constraint flags should not indicate that chroma-relatedcoding tools may be used in the bitstream when no chroma components areused in pictures of the bitstream. Similarly, the intraprediction-related constraint flags should not indicate that interprediction-related coding tools may be used in the bitstream when thebitstream only includes I slices. If a video coder is not configured touse a chroma-related coding tool or inter prediction-related codingtool, providing an indication that the chroma-related coding tool or theinter prediction-related coding tool may be used in the bitstream whenthe chroma-related coding tool or inter prediction-related coding toolmay not actually be used in the bitstream may cause the video decoder orother device to erroneously determine that the video decoder is unableto decode the bitstream. This may limit the functionality of the videodecoder.

To address this technical issue, this disclosure describes techniquesthat impose specific constraints on the values of chroma-relatedconstraint flags and inter prediction-related constraint flags. Theseconstraints may be verified in a bitstream conformance process. Thus, inaccordance with one or more techniques of this disclosure, a device mayperform a bitstream conformance process that determines whether abitstream that comprises an encoded representation of the video dataconforms to a video coding standard. The bitstream conformance processdetermines that the bitstream does not conform to the video codingstandard when at least one of: a chroma-related constraint flag is equalto 0 and when there are no chroma components for pictures in thebitstream, or an inter prediction-related constraint flag is equal to 0when all slices of the bitstream are I slices. In some examples, if thebitstream does not conform to the video coding standard, the device doesnot forward the bitstream to a video decoder for decoding.

FIG. 1 is a block diagram illustrating an example video encoding anddecoding system 100 that may perform the techniques of this disclosure.The techniques of this disclosure are generally directed to coding(encoding and/or decoding) video data. In general, video data includesany data for processing a video. Thus, video data may include raw,unencoded video, encoded video, decoded (e.g., reconstructed) video, andvideo metadata, such as signaling data.

As shown in FIG. 1 , system 100 includes a source device 102 thatprovides encoded video data to be decoded and displayed by a destinationdevice 116, in this example. In particular, source device 102 providesthe video data to destination device 116 via a computer-readable medium110. Source device 102 and destination device 116 may comprise any of awide range of devices, including desktop computers, notebook (i.e.,laptop) computers, tablet computers, set-top boxes, telephone handsetssuch as smartphones, televisions, cameras, display devices, digitalmedia players, video gaming consoles, video streaming device, or thelike. In some cases, source device 102 and destination device 116 may beequipped for wireless communication, and thus may be referred to aswireless communication devices.

In the example of FIG. 1 , source device 102 includes video source 104,memory 106, video encoder 200, and output interface 108. Destinationdevice 116 includes input interface 122, video decoder 300, memory 120,and display device 118. In accordance with this disclosure, videoencoder 200 of source device 102 and video decoder 300 of destinationdevice 116 may be configured to apply the techniques related to generalconstraint information syntax in video coding. Thus, source device 102represents an example of a video encoding device, while destinationdevice 116 represents an example of a video decoding device. In otherexamples, a source device and a destination device may include othercomponents or arrangements. For example, source device 102 may receivevideo data from an external video source, such as an external camera.Likewise, destination device 116 may interface with an external displaydevice, rather than include an integrated display device.

System 100 as shown in FIG. 1 is merely one example. In general, anydigital video encoding and/or decoding device may perform techniquesrelated to general constraint information syntax in video coding. Sourcedevice 102 and destination device 116 are merely examples of such codingdevices in which source device 102 generates coded video data fortransmission to destination device 116. This disclosure refers to a“coding” device as a device that performs coding (encoding and/ordecoding) of data. Thus, video encoder 200 and video decoder 300represent examples of coding devices, in particular, a video encoder anda video decoder, respectively. In some examples, source device 102 anddestination device 116 may operate in a substantially symmetrical mannersuch that each of source device 102 and destination device 116 includesvideo encoding and decoding components. Hence, system 100 may supportone-way or two-way video transmission between source device 102 anddestination device 116, e.g., for video streaming, video playback, videobroadcasting, or video telephony.

In general, video source 104 represents a source of video data (i.e.,raw, unencoded video data) and provides a sequential series of pictures(also referred to as “frames”) of the video data to video encoder 200,which encodes data for the pictures. Video source 104 of source device102 may include a video capture device, such as a video camera, a videoarchive containing previously captured raw video, and/or a video feedinterface to receive video from a video content provider. As a furtheralternative, video source 104 may generate computer graphics-based dataas the source video, or a combination of live video, archived video, andcomputer-generated video. In each case, video encoder 200 encodes thecaptured, pre-captured, or computer-generated video data. Video encoder200 may rearrange the pictures from the received order (sometimesreferred to as “display order”) into a coding order for coding. Videoencoder 200 may generate a bitstream including encoded video data.Source device 102 may then output the encoded video data via outputinterface 108 onto computer-readable medium 110 for reception and/orretrieval by, e.g., input interface 122 of destination device 116.

Memory 106 of source device 102 and memory 120 of destination device 116represent general purpose memories. In some examples, memories 106, 120may store raw video data, e.g., raw video from video source 104 and raw,decoded video data from video decoder 300. Additionally oralternatively, memories 106, 120 may store software instructionsexecutable by, e.g., video encoder 200 and video decoder 300,respectively. Although memory 106 and memory 120 are shown separatelyfrom video encoder 200 and video decoder 300 in this example, it shouldbe understood that video encoder 200 and video decoder 300 may alsoinclude internal memories for functionally similar or equivalentpurposes. Furthermore, memories 106, 120 may store encoded video data,e.g., output from video encoder 200 and input to video decoder 300. Inother words, memories 106, 120 may store a bitstream that comprises anencoded representation of video data. In some examples, portions ofmemories 106, 120 may be allocated as one or more video buffers, e.g.,to store raw, decoded, and/or encoded video data.

Computer-readable medium 110 may represent any type of medium or devicecapable of transporting the encoded video data from source device 102 todestination device 116. In one example, computer-readable medium 110represents a communication medium to enable source device 102 totransmit encoded video data directly to destination device 116 inreal-time, e.g., via a radio frequency network or computer-basednetwork. Output interface 108 may demodulate a transmission signalincluding the encoded video data, and input interface 122 may demodulatethe received transmission signal, according to a communication standard,such as a wireless communication protocol. The communication medium maycomprise any wireless or wired communication medium, such as a radiofrequency (RF) spectrum or one or more physical transmission lines. Thecommunication medium may form part of a packet-based network, such as alocal area network, a wide-area network, or a global network such as theInternet. The communication medium may include routers, switches, basestations, or any other equipment that may be useful to facilitatecommunication from source device 102 to destination device 116.

In some examples, source device 102 may output encoded data from outputinterface 108 to storage device 112. Similarly, destination device 116may access encoded data from storage device 112 via input interface 122.Storage device 112 may include any of a variety of distributed orlocally accessed data storage media such as a hard drive, Blu-ray discs,DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or anyother suitable digital storage media for storing encoded video data.

In some examples, source device 102 may output encoded video data tofile server 114 or another intermediate storage device that may storethe encoded video data generated by source device 102. Destinationdevice 116 may access stored video data from file server 114 viastreaming or download. File server 114 may be any type of server devicecapable of storing encoded video data and transmitting that encodedvideo data to the destination device 116. File server 114 may representa web server (e.g., for a website), a File Transfer Protocol (FTP)server, a content delivery network device, or a network attached storage(NAS) device. Destination device 116 may access encoded video data fromfile server 114 through any standard data connection, including anInternet connection. This may include a wireless channel (e.g., a Wi-Ficonnection), a wired connection (e.g., digital subscriber line (DSL),cable modem, etc.), or a combination of both that is suitable foraccessing encoded video data stored on file server 114. File server 114and input interface 122 may be configured to operate according to astreaming transmission protocol, a download transmission protocol, or acombination thereof.

Output interface 108 and input interface 122 may represent wirelesstransmitters/receivers, modems, wired networking components (e.g.,Ethernet cards), wireless communication components that operateaccording to any of a variety of IEEE 802.11 standards, or otherphysical components. In examples where output interface 108 and inputinterface 122 comprise wireless components, output interface 108 andinput interface 122 may be configured to transfer data, such as encodedvideo data, according to a cellular communication standard, such as 4G,4G-LTE (Long-Term Evolution), LTE Advanced, 5G, or the like. In someexamples where output interface 108 comprises a wireless transmitter,output interface 108 and input interface 122 may be configured totransfer data, such as encoded video data, according to other wirelessstandards, such as an IEEE 802.11 specification, an IEEE 802.15specification (e.g., ZigBee™), a Bluetooth™ standard, or the like. Insome examples, source device 102 and/or destination device 116 mayinclude respective system-on-a-chip (SoC) devices. For example, sourcedevice 102 may include an SoC device to perform the functionalityattributed to video encoder 200 and/or output interface 108, anddestination device 116 may include an SoC device to perform thefunctionality attributed to video decoder 300 and/or input interface122.

The techniques of this disclosure may be applied to video coding insupport of any of a variety of multimedia applications, such asover-the-air television broadcasts, cable television transmissions,satellite television transmissions, Internet streaming videotransmissions, such as dynamic adaptive streaming over HTTP (DASH),digital video that is encoded onto a data storage medium, decoding ofdigital video stored on a data storage medium, or other applications.

Input interface 122 of destination device 116 receives an encoded videobitstream from computer-readable medium 110 (e.g., a communicationmedium, storage device 112, file server 114, or the like). The encodedvideo bitstream may include signaling information defined by videoencoder 200, which is also used by video decoder 300, such as syntaxelements having values that describe characteristics and/or processingof video blocks or other coded units (e.g., slices, pictures, groups ofpictures, sequences, or the like). Display device 118 displays decodedpictures of the decoded video data to a user. Display device 118 mayrepresent any of a variety of display devices such as a cathode ray tube(CRT), a liquid crystal display (LCD), a plasma display, an organiclight emitting diode (OLED) display, or another type of display device.

Although not shown in FIG. 1 , in some examples, video encoder 200 andvideo decoder 300 may each be integrated with an audio encoder and/oraudio decoder, and may include appropriate MUX-DEMUX units, or otherhardware and/or software, to handle multiplexed streams including bothaudio and video in a common data stream. If applicable, MUX-DEMUX unitsmay conform to the ITU H.223 multiplexer protocol, or other protocolssuch as the user datagram protocol (UDP).

Video encoder 200 and video decoder 300 each may be implemented as anyof a variety of suitable encoder and/or decoder circuitry, such as oneor more microprocessors, digital signal processors (DSPs), applicationspecific integrated circuits (ASICs), field programmable gate arrays(FPGAs), discrete logic, software, hardware, firmware or anycombinations thereof. When the techniques are implemented partially insoftware, a device may store instructions for the software in asuitable, non-transitory computer-readable medium and execute theinstructions in hardware using one or more processors to perform thetechniques of this disclosure. Each of video encoder 200 and videodecoder 300 may be included in one or more encoders or decoders, eitherof which may be integrated as part of a combined encoder/decoder (CODEC)in a respective device. A device including video encoder 200 and/orvideo decoder 300 may comprise an integrated circuit, a microprocessor,and/or a wireless communication device, such as a cellular telephone.

Video encoder 200 and video decoder 300 may operate according to a videocoding standard, such as ITU-T H.265, also referred to as HighEfficiency Video Coding (HEVC) or extensions thereto, such as themulti-view and/or scalable video coding extensions. Alternatively, videoencoder 200 and video decoder 300 may operate according to otherproprietary or industry standards, such as ITU-T H.266, also referred toas Versatile Video Coding (VVC). A recent draft of the VVC standard isdescribed in Bross, et al. “Versatile Video Coding (Draft 8),” JointVideo Experts Team (JVET) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG11, 17^(th) Meeting: Brussels, BE, 7-17 Jan. 2020, JVET-Q2001-vE(hereinafter “VVC Draft 8”). The reference software is called VVC TestModel (VTM). Subclause 7.3.3.2 and Subclause 7.4.4.2 in VVC Draft 8version 15 are investigated and improved in this disclosure. There areseveral proposed changes in this disclosure. At least one proposedchange below or a combination of at least two proposed changes below canbe applied to the current VVC Working Draft, i.e., JVET-Q2001. Thetechniques of this disclosure, however, are not limited to anyparticular coding standard.

In general, video encoder 200 and video decoder 300 may performblock-based coding of pictures. The term “block” generally refers to astructure including data to be processed (e.g., encoded, decoded, orotherwise used in the encoding and/or decoding process). For example, ablock may include a two-dimensional matrix of samples of luminanceand/or chrominance data. In general, video encoder 200 and video decoder300 may code video data represented in a YUV (e.g., Y, Cb, Cr) format.That is, rather than coding red, green, and blue (RGB) data for samplesof a picture, video encoder 200 and video decoder 300 may code luminanceand chrominance components, where the chrominance components may includeboth red hue and blue hue chrominance components. In some examples,video encoder 200 converts received RGB formatted data to a YUVrepresentation prior to encoding, and video decoder 300 converts the YUVrepresentation to the RGB format. Alternatively, pre- andpost-processing units (not shown) may perform these conversions.

This disclosure may generally refer to coding (e.g., encoding anddecoding) of pictures to include the process of encoding or decodingdata of the picture. Similarly, this disclosure may refer to coding ofblocks of a picture to include the process of encoding or decoding datafor the blocks, e.g., prediction and/or residual coding. An encodedvideo bitstream generally includes a series of values for syntaxelements representative of coding decisions (e.g., coding modes) andpartitioning of pictures into blocks. Thus, references to coding apicture or a block should generally be understood as coding values forsyntax elements forming the picture or block.

HEVC defines various blocks, including coding units (CUs), predictionunits (PUs), and transform units (TUs). According to HEVC, a video coder(such as video encoder 200) partitions a coding tree unit (CTU) into CUsaccording to a quadtree structure. That is, the video coder partitionsCTUs and CUs into four equal, non-overlapping squares, and each node ofthe quadtree has either zero or four child nodes. Nodes without childnodes may be referred to as “leaf nodes,” and CUs of such leaf nodes mayinclude one or more PUs and/or one or more TUs. The video coder mayfurther partition PUs and TUs. For example, in HEVC, a residual quadtree(RQT) represents partitioning of TUs. In HEVC, PUs representinter-prediction data, while TUs represent residual data. CUs that areintra-predicted include intra-prediction information, such as anintra-mode indication.

As another example, video encoder 200 and video decoder 300 may beconfigured to operate according to VVC. According to VVC, a video coder(such as video encoder 200) partitions a picture into a plurality ofcoding tree units (CTUs). Video encoder 200 may partition a CTUaccording to a tree structure, such as a quadtree-binary tree (QTBT)structure or Multi-Type Tree (MTT) structure. The QTBT structure removesthe concepts of multiple partition types, such as the separation betweenCUs, PUs, and TUs of HEVC. A QTBT structure includes two levels: a firstlevel partitioned according to quadtree partitioning, and a second levelpartitioned according to binary tree partitioning. A root node of theQTBT structure corresponds to a CTU. Leaf nodes of the binary treescorrespond to coding units (CUs).

In an MTT partitioning structure, blocks may be partitioned using aquadtree (QT) partition, a binary tree (BT) partition, and one or moretypes of triple tree (TT) (also called ternary tree (TT)) partitions. Atriple or ternary tree partition is a partition where a block is splitinto three sub-blocks. In some examples, a triple or ternary treepartition divides a block into three sub-blocks without dividing theoriginal block through the center. The partitioning types in MTT (e.g.,QT, BT, and TT), may be symmetrical or asymmetrical.

In some examples, video encoder 200 and video decoder 300 may use asingle QTBT or MTT structure to represent each of the luminance andchrominance components, while in other examples, video encoder 200 andvideo decoder 300 may use two or more QTBT or MTT structures, such asone QTBT/MTT structure for the luminance component and another QTBT/MTTstructure for both chrominance components (or two QTBT/MTT structuresfor respective chrominance components).

Video encoder 200 and video decoder 300 may be configured to usequadtree partitioning per HEVC, QTBT partitioning, MTT partitioning, orother partitioning structures. For purposes of explanation, thedescription of the techniques of this disclosure is presented withrespect to QTBT partitioning. However, it should be understood that thetechniques of this disclosure may also be applied to video codersconfigured to use quadtree partitioning, or other types of partitioningas well.

In some examples, a CTU includes a coding tree block (CTB) of lumasamples, two corresponding CTBs of chroma samples of a picture that hasthree sample arrays, or a CTB of samples of a monochrome picture or apicture that is coded using three separate color planes and syntaxstructures used to code the samples. A CTB may be an N×N block ofsamples for some value of N such that the division of a component intoCTBs is a partitioning. A component is an array or single sample fromone of the three arrays (luma and two chroma) that compose a picture in4:2:0, 4:2:2, or 4:4:4 color format or the array or a single sample ofthe array that compose a picture in monochrome format. In some examples,a coding block is an M×N block of samples for some values of M and Nsuch that a division of a CTB into coding blocks is a partitioning.

The blocks (e.g., CTUs or CUs) may be grouped in various ways in apicture. As one example, a brick may refer to a rectangular region ofCTU rows within a particular tile in a picture. A tile may be arectangular region of CTUs within a particular tile column and aparticular tile row in a picture. A tile column refers to a rectangularregion of CTUs having a height equal to the height of the picture and awidth specified by syntax elements (e.g., such as in a picture parameterset). A tile row refers to a rectangular region of CTUs having a heightspecified by syntax elements (e.g., such as in a picture parameter set)and a width equal to the width of the picture.

In some examples, a tile may be partitioned into multiple bricks, eachof which may include one or more CTU rows within the tile. A tile thatis not partitioned into multiple bricks may also be referred to as abrick. However, a brick that is a true subset of a tile may not bereferred to as a tile.

The bricks in a picture may also be arranged in a slice. A slice may bean integer number of bricks of a picture that may be exclusivelycontained in a single network abstraction layer (NAL) unit. In someexamples, a slice includes either a number of complete tiles or only aconsecutive sequence of complete bricks of one tile.

This disclosure may use “N×N” and “N by N” interchangeably to refer tothe sample dimensions of a block (such as a CU or other video block) interms of vertical and horizontal dimensions, e.g., 16×16 samples or 16by 16 samples. In general, a 16×16 CU will have 16 samples in a verticaldirection (y=16) and 16 samples in a horizontal direction (x=16).Likewise, an N×N CU generally has N samples in a vertical direction andN samples in a horizontal direction, where N represents a nonnegativeinteger value. The samples in a CU may be arranged in rows and columns.Moreover, CUs need not necessarily have the same number of samples inthe horizontal direction as in the vertical direction. For example, CUsmay comprise N×M samples, where M is not necessarily equal to N.

Video encoder 200 encodes video data for CUs representing predictionand/or residual information, and other information. The predictioninformation indicates how the CU is to be predicted in order to form aprediction block for the CU. The residual information generallyrepresents sample-by-sample differences between samples of the CU priorto encoding and the prediction block.

To predict a CU, video encoder 200 may generally form a prediction blockfor the CU through inter-prediction or intra-prediction.Inter-prediction generally refers to predicting the CU from data of apreviously coded picture, whereas intra-prediction generally refers topredicting the CU from previously coded data of the same picture. Toperform inter-prediction, video encoder 200 may generate the predictionblock using one or more motion vectors. Video encoder 200 may generallyperform a motion search to identify a reference block that closelymatches the CU, e.g., in terms of differences between the CU and thereference block. Video encoder 200 may calculate a difference metricusing a sum of absolute difference (SAD), sum of squared differences(SSD), mean absolute difference (MAD), mean squared differences (MSD),or other such difference calculations to determine whether a referenceblock closely matches the current CU. In some examples, video encoder200 may predict the current CU using uni-directional prediction orbi-directional prediction.

Some examples of VVC also provide an affine motion compensation mode,which may be considered an inter-prediction mode. In affine motioncompensation mode, video encoder 200 may determine two or more motionvectors that represent non-translational motion, such as zoom in or out,rotation, perspective motion, or other irregular motion types.

To perform intra-prediction, video encoder 200 may select anintra-prediction mode to generate the prediction block. Some examples ofVVC provide sixty-seven intra-prediction modes, including variousdirectional modes, as well as planar mode and DC mode. In general, videoencoder 200 selects an intra-prediction mode that describes neighboringsamples to a current block (e.g., a block of a CU) from which to predictsamples of the current block. Such samples may generally be above, aboveand to the left, or to the left of the current block in the same pictureas the current block, assuming video encoder 200 codes CTUs and CUs inraster scan order (left to right, top to bottom).

Video encoder 200 encodes data representing the prediction mode for acurrent block. For example, for inter-prediction modes, video encoder200 may encode data representing which of the various availableinter-prediction modes is used, as well as motion information for thecorresponding mode. For uni-directional or bi-directionalinter-prediction, for example, video encoder 200 may encode motionvectors using advanced motion vector prediction (AMVP) or merge mode.Video encoder 200 may use similar modes to encode motion vectors foraffine motion compensation mode.

Following prediction, such as intra-prediction or inter-prediction of ablock, video encoder 200 may calculate residual data for the block. Theresidual data, such as a residual block, represents sample by sampledifferences between the block and a prediction block for the block,formed using the corresponding prediction mode. Video encoder 200 mayapply one or more transforms to the residual block, to producetransformed data in a transform domain instead of the sample domain. Forexample, video encoder 200 may apply a discrete cosine transform (DCT),an integer transform, a wavelet transform, or a conceptually similartransform to residual video data. Additionally, video encoder 200 mayapply a secondary transform following the first transform, such as amode-dependent non-separable secondary transform (MDNSST), a signaldependent transform, a Karhunen-Loeve transform (KLT), or the like.Video encoder 200 produces transform coefficients following applicationof the one or more transforms.

As noted above, following any transforms to produce transformcoefficients, video encoder 200 may perform quantization of thetransform coefficients. Quantization generally refers to a process inwhich transform coefficients are quantized to possibly reduce the amountof data used to represent the transform coefficients, providing furthercompression. By performing the quantization process, video encoder 200may reduce the bit depth associated with some or all of the transformcoefficients. For example, video encoder 200 may round an n-bit valuedown to an m-bit value during quantization, where n is greater than m.In some examples, to perform quantization, video encoder 200 may performa bitwise right-shift of the value to be quantized.

Following quantization, video encoder 200 may scan the transformcoefficients, producing a one-dimensional vector from thetwo-dimensional matrix including the quantized transform coefficients.The scan may be designed to place higher energy (and therefore lowerfrequency) transform coefficients at the front of the vector and toplace lower energy (and therefore higher frequency) transformcoefficients at the back of the vector. In some examples, video encoder200 may utilize a predefined scan order to scan the quantized transformcoefficients to produce a serialized vector, and then entropy encode thequantized transform coefficients of the vector. In other examples, videoencoder 200 may perform an adaptive scan. After scanning the quantizedtransform coefficients to form the one-dimensional vector, video encoder200 may entropy encode the one-dimensional vector, e.g., according tocontext-adaptive binary arithmetic coding (CABAC). Video encoder 200 mayalso entropy encode values for syntax elements describing metadataassociated with the encoded video data for use by video decoder 300 indecoding the video data.

To perform CABAC, video encoder 200 may assign a context within acontext model to a symbol to be transmitted. The context may relate to,for example, whether neighboring values of the symbol are zero-valued ornot. The probability determination may be based on a context assigned tothe symbol.

Video encoder 200 may further generate syntax data, such as block-basedsyntax data, picture-based syntax data, and sequence-based syntax data,to video decoder 300, e.g., in a picture header, a block header, a sliceheader, or other syntax data, such as a sequence parameter set (SPS),picture parameter set (PPS), or video parameter set (VPS). Video decoder300 may likewise decode such syntax data to determine how to decodecorresponding video data.

In this manner, video encoder 200 may generate a bitstream includingencoded video data, e.g., syntax elements describing partitioning of apicture into blocks (e.g., CUs) and prediction and/or residualinformation for the blocks. Ultimately, video decoder 300 may receivethe bitstream and decode the encoded video data.

In general, video decoder 300 performs a reciprocal process to thatperformed by video encoder 200 to decode the encoded video data of thebitstream. For example, video decoder 300 may decode values for syntaxelements of the bitstream using CABAC in a manner substantially similarto, albeit reciprocal to, the CABAC encoding process of video encoder200. The syntax elements may define partitioning information forpartitioning of a picture into CTUs, and partitioning of each CTUaccording to a corresponding partition structure, such as a QTBTstructure, to define CUs of the CTU. The syntax elements may furtherdefine prediction and residual information for blocks (e.g., CUs) ofvideo data.

The residual information may be represented by, for example, quantizedtransform coefficients. Video decoder 300 may inverse quantize andinverse transform the quantized transform coefficients of a block toreproduce a residual block for the block. Video decoder 300 uses asignaled prediction mode (intra- or inter-prediction) and relatedprediction information (e.g., motion information for inter-prediction)to form a prediction block for the block. Video decoder 300 may thencombine the prediction block and the residual block (on asample-by-sample basis) to reproduce the original block. Video decoder300 may perform additional processing, such as performing a deblockingprocess to reduce visual artifacts along boundaries of the block.

This disclosure may generally refer to “signaling” certain information,such as syntax elements. The term “signaling” may generally refer to thecommunication of values for syntax elements and/or other data used todecode encoded video data. That is, video encoder 200 may signal valuesfor syntax elements in the bitstream. In general, signaling refers togenerating a value in the bitstream. As noted above, source device 102may transport the bitstream to destination device 116 substantially inreal time, or not in real time, such as might occur when storing syntaxelements to storage device 112 for later retrieval by destination device116.

FIGS. 2A and 2B are conceptual diagrams illustrating an example quadtreebinary tree (QTBT) structure 130, and a corresponding coding tree unit(CTU) 132. The solid lines represent quadtree splitting, and dottedlines indicate binary tree splitting. In each split (i.e., non-leaf)node of the binary tree, one flag is signaled to indicate whichsplitting type (i.e., horizontal or vertical) is used, where 0 indicateshorizontal splitting and 1 indicates vertical splitting in this example.For the quadtree splitting, there is no need to indicate the splittingtype, because quadtree nodes split a block horizontally and verticallyinto 4 sub-blocks with equal size. Accordingly, video encoder 200 mayencode, and video decoder 300 may decode, syntax elements (such assplitting information) for a region tree level of QTBT structure 130(i.e., the solid lines) and syntax elements (such as splittinginformation) for a prediction tree level of QTBT structure 130 (i.e.,the dashed lines). Video encoder 200 may encode, and video decoder 300may decode, video data, such as prediction and transform data, for CUsrepresented by terminal leaf nodes of QTBT structure 130.

In general, CTU 132 of FIG. 2B may be associated with parametersdefining sizes of blocks corresponding to nodes of QTBT structure 130 atthe first and second levels. These parameters may include a CTU size(representing a size of CTU 132 in samples), a minimum quadtree size(MinQTSize, representing a minimum allowed quadtree leaf node size), amaximum binary tree size (MaxBTSize, representing a maximum allowedbinary tree root node size), a maximum binary tree depth (MaxBTDepth,representing a maximum allowed binary tree depth), and a minimum binarytree size (MinBTSize, representing the minimum allowed binary tree leafnode size).

The root node of a QTBT structure corresponding to a CTU may have fourchild nodes at the first level of the QTBT structure, each of which maybe partitioned according to quadtree partitioning. That is, nodes of thefirst level are either leaf nodes (having no child nodes) or have fourchild nodes. The example of QTBT structure 130 represents such nodes asincluding the parent node and child nodes having solid lines forbranches. If nodes of the first level are not larger than the maximumallowed binary tree root node size (MaxBTSize), then the nodes can befurther partitioned by respective binary trees. The binary treesplitting of one node can be iterated until the nodes resulting from thesplit reach the minimum allowed binary tree leaf node size (MinBTSize)or the maximum allowed binary tree depth (MaxBTDepth). The example ofQTBT structure 130 represents such nodes as having dashed lines forbranches. The binary tree leaf node is referred to as a coding unit(CU), which is used for prediction (e.g., intra-picture or inter-pictureprediction) and transform, without any further partitioning. Asdiscussed above, CUs may also be referred to as “video blocks” or“blocks.”

In one example of the QTBT partitioning structure, the CTU size is setas 128×128 (luma samples and two corresponding 64×64 chroma samples),the MinQTSize is set as 16×16, the MaxBTSize is set as 64×64, theMinBTSize (for both width and height) is set as 4, and the MaxBTDepth isset as 4. The quadtree partitioning is applied to the CTU first togenerate quad-tree leaf nodes. The quadtree leaf nodes may have a sizefrom 16×16 (i.e., the MinQTSize) to 128×128 (i.e., the CTU size). If thequadtree leaf node is 128×128, the leaf quadtree node will not befurther split by the binary tree, because the size exceeds the MaxBTSize(i.e., 64×64, in this example). Otherwise, the quadtree leaf node willbe further partitioned by the binary tree. Therefore, the quadtree leafnode is also the root node for the binary tree and has the binary treedepth as 0. When the binary tree depth reaches MaxBTDepth (4, in thisexample), no further splitting is permitted. When the binary tree nodehas a width equal to MinBTSize (4, in this example), it implies that nofurther vertical splitting is permitted. Similarly, a binary tree nodehaving a height equal to MinBTSize implies that no further horizontalsplitting is permitted for that binary tree node. As noted above, leafnodes of the binary tree are referred to as CUs and are furtherprocessed according to prediction and transform without furtherpartitioning.

As mentioned above, if a video coder is not configured to use achroma-related coding tool or inter prediction-related coding tool,providing an indication that the chroma-related coding tool or the interprediction-related coding tool may be used in the bitstream when thechroma-related coding tool or inter prediction-related coding tool maynot actually be used in the bitstream may cause the video decoder orother device to erroneously determine that the video decoder is unableto decode the bitstream. This may limit the functionality of the videodecoder. This disclosure provides several proposals to improve thegeneral constraint information syntax:

-   -   (1) Semantics improvement for general constraint flags. This        disclosure describes two example solutions:        -   a. Solution 1: Remove the bitstream conformance “When            one_slice_per_pic_constraint_flag is equal to 1, the value            of one_subpic_per_pic_constraint_flag shall be equal to 1”.        -   b. Solution 2: Constrain the chroma-related constraint flags            to be equal to 1 when max_chroma_format_constraint_idc is            equal to 0 (i.e., when there are no chroma components).            Constrain the inter prediction-related constraint flags to            be equal to 1 when intra_only_constraint_flag is equal to 1            (i.e., when slice_type are I for all slices).

(2) Add general constraint flags for the coding tools.

(3) Add general constraint flags for the single layer and singlesublayer.

(4) Add general constraint flags for the VPS and PH.

In VVC Draft 8, one_slice_per_pic_constraint_flag equal to 1 specifiesthat each picture shall contain only one slice.one_slice_per_pic_constraint_flag equal to 0 does not impose such aconstraint. Furthermore, in VVC Draft 8,one_subpic_per_pic_constraint_flag equal to 1 specifies that eachpicture shall contain only one subpicture.one_subpic_per_pic_constraint_flag equal to 0 does not impose such aconstraint. When one_slice_per_pic_constraint_flag is equal to 1, thevalue of one_subpic_per_pic_constraint_flag shall be equal to 1.

In the current general constraint syntax design, there is a bitstreamconformance to constrain one_subpic_per_pic_constraint_flag byone_slice_per_pic_constraint_flag as follows:

-   -   When one_slice_per_pic_constraint_flag is equal to 1, the value        of one_subpic_per_pic_constraint_flag shall be equal to 1.

If there is no such conformance constraint toone_subpic_per_pic_constraint_flag, there is no bug (error) to videodecoder 300 from high-level parameter sets to low-level decodingprocess, but it might be beneficial to avoid a product to set up aprofile which is not reasonable at all. Therefore, this proposalprovides two examples to address the issue:

Example 1

Remove the bitstream conformance “When one_slice_per_pic_constraint_flagis equal to 1, the value of one_subpic_per_pic_constraint_flag shall beequal to 1”.

Thus, in some such examples, a device (e.g., source device 102,destination device 116, etc.) may perform a bitstream conformanceprocess that determines whether a bitstream that comprises an encodedrepresentation of the video data conforms to a video coding standard,wherein the bitstream conformance process determines that the bitstreamdoes not conform to the video coding standard when a chroma-relatedconstraint flag is equal to 0 and when there are no chroma componentsfor pictures in the bitstream.

Example 2

Constrain the chroma-related constraint flags to be equal to 1 whenmax_chroma_format_constraint_idc is equal to 0 (i.e., when there is nochroma components). Constrain the inter prediction-related constraintflags to be equal to 1 when intra_only_constraint_flag is equal to 1(i.e., when slice_type shall be I for all slices). The proposed changesto VVC 8 are shown by the <!> . . . </!> tags as follows in Table 1:

TABLE 1 no_qtbtt_dual_tree_intra_constraint_flag equal to 1 specifiesthat qtbtt_dual_tree_intra_flag shall be equal to 0.no_qtbtt_dual_tree_intra_constraint_flag equal to 0 does not impose sucha constraint. <!>When max_chroma_format_constraint_idc is equal to 0,the value of no_qtbtt_dual_tree_intra_constraint_flag shall be equal to1.</!> no_ccalf_constraint_flag equal to 1 specifies thatsps_ccalf_enabled_flag shall be equal to 0. no_ccalf_constraint_flagequal to 0 does not impose such a constraint. <!>Whenmax_chroma_format_constraint_idc is equal to 0, the value ofno_ccalf_constraint_flag shall be equal to 1.</!>no_joint_cbcr_constraint_flag equal to 1 specifies thatsps_joint_cbcr_enabled_flag shall be equal to 0.no_joint_cbcr_constraint_flag equal to 0 does not impose such aconstraint. <!>When max_chroma_format_constraint_idc is equal to 0, thevalue of no_joint_cbcr_constraint_flag shall be equal to 1.</!>no_ref_wraparound_constraint_flag equal to 1 specifies thatsps_ref_wraparound_enabled_flag shall be equal to 0.no_ref_wraparound_constraint_flag equal to 0 does not impose such aconstraint. <!>When intra_only_constraint_flag is equal to 1, the valueof no_ref_wraparound_constraint_flag shall be equal to 1.</!>no_temporal_mvp_constraint_flag equal to 1 specifies thatsps_temporal_mvp_enabled_flag shall be equal to 0.no_temporal_mvp_constraint_flag equal to 0 does not impose such aconstraint. <!>When intra_only_constraint_flag is equal to 1, the valueof no_temporal_mvp_constraint_flag shall be equal to 1.</!>no_sbtmvp_constraint_flag equal to 1 specifies thatsps_sbtmvp_enabled_flag shall be equal to 0. no_sbtmvp_constraint_flagequal to 0 does not impose such a constraint. <!>Whenintra_only_constraint_flag is equal to 1, the value ofno_sbtmvp_constraint_flag shall be equal to 1.</!>no_amvr_constraint_flag equal to 1 specifies that sps_amvr_enabled_flagshall be equal to 0. no_amvr_constraint_flag equal to 0 does not imposesuch a constraint. <!>When intra_only_constraint_flag is equal to 1, thevalue of no_amvr_constraint_flag shall be equal to 1.</!>no_bdof_constraint_flag equal to 1 specifies that sps_bdof_enabled_flagshall be equal to 0. no_bdof_constraint_flag equal to 0 does not imposesuch a constraint. <!>When intra_only_constraint_flag is equal to 1, thevalue of no_bdof_constraint_flag shall be equal to 1.</!>no_dmvr_constraint_flag equal to 1 specifies that sps_dmvr_enabled_flagshall be equal to 0. no_dmvr_constraint_flag equal to 0 does not imposesuch a constraint. <!>When intra_only_constraint_flag is equal to 1, thevalue of no_dmvr_constraint_flag shall be equal to 1.</!>no_cclm_constraint_flag equal to 1 specifies that sps_cclm_enabled_flagshall be equal to 0. no_cclm_constraint_flag equal to 0 does not imposesuch a constraint. <!>When max_chroma_format_constraint_idc is equal to0, the value of no_cclm_constraint_flag shall be equal to 1.</!>no_affine_motion_constraint_flag equal to 1 specifies thatsps_affine_enabled_flag shall be equal to 0.no_affine_motion_constraint_flag equal to 0 does not impose such aconstraint. <!>When intra_only_constraint_flag is equal to 1, the valueof no_affine_motion_constraint_flag shall be equal to 1.</!>no_bcw_constraint_flag equal to 1 specifies that sps_bcw_enabled_flagshall be equal to 0. no_bcw_constraint_flag equal to 0 does not imposesuch a constraint. <!>When intra_only_constraint_flag is equal to 1, thevalue of no_bcw_constraint_flag shall be equal to 1.</!>no_ciip_constraint_flag equal to 1 specifies that sps_ciip_enabled_flagshall be equal to 0. no_cipp_constraint_flag equal to 0 does not imposesuch a constraint. <!>When intra_only_constraint_flag is equal to 1, thevalue of no_cipp_constraint_flag shall be equal to 1.</!>no_fpel_mmvd_constraint_flag equal to 1 specifies thatsps_fpel_mmvd_enabled_flag shall be equal to 0.no_fpel_mmvd_constraint_flag equal to 0 does not impose such aconstraint. <!>When intra_only_constraint_flag is equal to 1, the valueof no_fpel_mmvd_constraint_flag shall be equal to 1.</!>no_gpm_constraint_flag equal to 1 specifies that sps_gpm_enabled_flagshall be equal to 0. no_gpm_constraint_flag equal to 0 does not imposesuch a constraint. <!>When intra_only_constraint_flag is equal to 1, thevalue of no_gpm_constraint_flag shall be equal to 1.</!>

The semantics of syntax elements mentioned in Table 1, above areprovided in Table 2, below.

TABLE 2 qtbtt_dual_tree_intra_flag equal to 1 specifies that, for Islices, each CTU is split into coding units with 64×64 luma samplesusing an implicit quadtree split, and these coding units are the root oftwo separate coding_tree syntax structure for luma and chroma.qtbtt_dual_tree_intra_flag equal to 0 specifies separate coding_treesyntax structure is not used for I slices. Whenqtbtt_dual_tree_intra_flag is not present, it is inferred to be equal to0. sps_ccalf_enabled_flag equal to 0 specifies that the cross-componentadaptive loop filter is disabled. sps_ccalf_enabled_flag equal to 1specifies that the cross- component adaptive loop filter may be enabled.max_chroma_format_constraint_idc specifies that chroma_format_idc shallbe in the range of 0 to max_chroma_format_constraint_idc, inclusive.sps_joint_cbcr_enabled_flag equal to 0 specifies that the joint codingof chroma residuals is disabled. sps_joint_cbcr_enabled_flag equal to 1specifies that the joint coding of chroma residuals is enabled. When notpresent, the value of sps_joint_cbcr_enabled_flag is inferred to beequal to 0. sps_ref_wraparound_enabled_flag equal to 1 specifies thathorizontal wrap-around motion compensation is applied in interprediction. sps_ref_wraparound_enabled_flag equal to 0 specifies thathorizontal wrap-around motion compensation is not applied.intra_only_constraint_flag equal to 1 specifies that slice_type shall beequal to I. intra_only_constraint_flag equal to 0 does not impose such aconstraint. sps_temporal_mvp_enabled_flag equal to 1 specifies thattemporal motion vector predictors may be used in the CLVS.sps_temporal_mvp_enabled_flag equal to 0 specifies that temporal motionvector predictors are not used in the CLVS. sps_sbtmvp_enabled_flagequal to 1 specifies that subblock-based temporal motion vectorpredictors may be used in decoding of pictures with all slices havingslice_type not equal to I in the CLVS. sps_sbtmvp_enabled_flag equal to0 specifies that subblock-based temporal motion vector predictors arenot used in the CLVS. When sps_sbtmvp_enabled_flag is not present, it isinferred to be equal to 0. sps_amvr_enabled_flag equal to 1 specifiesthat adaptive motion vector difference resolution is used in motionvector coding. amvr_enabled_flag equal to 0 specifies that adaptivemotion vector difference resolution is not used in motion vector coding.sps_bdof_enabled_flag equal to 0 specifies that the bi-directionaloptical flow inter prediction is disabled. sps_bdof_enabled_flag equalto 1 specifies that the bi- directional optical flow inter prediction isenabled. sps_dmvr_enabled_flag equal to 1 specifies that decoder motionvector refinement based inter bi-prediction is enabled.sps_dmvr_enabled_flag equal to 0 specifies that decoder motion vectorrefinement based inter bi-prediction is disabled.sps_affine_enabled_flag specifies whether affine model based motioncompensation can be used for inter prediction. Ifsps_affine_enabled_flag is equal to 0, the syntax shall be constrainedsuch that no affine model based motion compensation is used in the CLVS,and inter_affine_flag and cu_affine_type_flag are not present in codingunit syntax of the CLVS. Otherwise (sps_affine_enabled_flag is equal to1), affine model based motion compensation can be used in the CLVS.sps_bcw_enabled_flag specifies whether bi-prediction with CU weights canbe used for inter prediction. If sps_bcw_enabled_flag is equal to 0, thesyntax shall be constrained such that no bi-prediction with CU weightsis used in the CLVS, and bcw_idx is not present in coding unit syntax ofthe CLVS. Otherwise (sps_bcw_enabled_flag is equal to 1), bi-predictionwith CU weights can be used in the CLVS. sps_ciip_enabled_flag specifiesthat ciip_flag may be present in the coding unit syntax for inter codingunits. sps_ciip_enabled_flag equal to 0 specifies that ciip_flag is notpresent in the coding unit syntax for inter coding units. ciip_flag[ x0][ y0 ] specifies whether the combined inter-picture merge and intra-picture prediction is applied for the current coding unit.sps_fpel_mmvd_enabled_flag equal to 1 specifies that merge mode withmotion vector difference is using integer sample precision.sps_fpel_mmvd_enabled_flag equal to 0 specifies that merge mode withmotion vector difference can use fractional sample precision.sps_gpm_enabled_flag specifies whether geometric partition based motioncompensation can be used for inter prediction. sps_gpm_enabled_flagequal to 0 specifies that the syntax shall be constrained such that nogeometric partition based motion compensation is used in the CLVS, andmerge_gpm_partition_idx, merge_gpm_idx0, and merge_gpm_idx1 are notpresent in coding unit syntax of the CLVS. sps_gpm_enabled_flag equal to1 specifies that geometric partition based motion compensation can beused in the CLVS. When not present, the value of sps_gpm_enabled_flag isinferred to be equal to 0.

Thus, in some such examples, a device (e.g., source device 102,destination device 116, etc.) may perform a bitstream conformanceprocess that determines whether a bitstream that comprises an encodedrepresentation of the video data conforms to a video coding standard,wherein the bitstream conformance process determines that the bitstreamdoes not conform to the video coding standard when a chroma-relatedconstraint flag is equal to 0 and when there are no chroma componentsfor pictures in the bitstream. In some examples, the device may performa bitstream conformance process that determines whether a bitstream thatcomprises an encoded representation of the video data conforms to avideo coding standard, wherein the bitstream conformance processdetermines that the bitstream does not conform to the video codingstandard when an inter prediction-related constraint flag is equal to 0when all slices of the bitstream are I slices.

In another example, the flags are conditioned bymax_chroma_format_constraint_idc=0 and intra_only_constraint_flag=1 asfollows:

-   -   The signalling of one_subpic_per_pic_constraint_flag is omitted        and inferred to be equal to 1 when        one_slice_per_pic_constraint_flag is equal to 1.    -   The signalling of no_qtbtt_dual_tree_intra_constraint_flag is        omitted and inferred to be equal to 1 when        max_chroma_format_constraint_idc is equal to 0.    -   The signalling of no_ccalf_constraint_flag is omitted and        inferred to be equal to 1 when max_chroma_format_constraint_idc        is equal to 0.    -   The signalling of no_joint_cbcr_constraint_flag is omitted and        inferred to be equal to 1 when max_chroma_format_constraint_idc        is equal to 0.    -   The signalling of no_cclm_constraint_flag is omitted and        inferred to be equal to 1 when max_chroma_format_constraint_idc        is equal to 0.    -   The signalling of no_ref_wraparound_constraint_flag is omitted        and inferred to be equal to 1 when intra_only_constraint_flag is        equal to 1.    -   The signalling of no_temporal_mvp_constraint_flag is omitted and        inferred to be equal to 1 when intra_only_constraint_flag is        equal to 1.    -   The signalling of no_sbtmvp_constraint_flag is omitted and        inferred to be equal to 1 when intra_only_constraint_flag is        equal to 1.    -   The signalling of no_amvr_constraint_flag is omitted and        inferred to be equal to 1 when intra_only_constraint_flag is        equal to 1.    -   The signalling of no_bdof_constraint_flag is omitted and        inferred to be equal to 1 when intra_only_constraint_flag is        equal to 1.    -   The signalling of no_dmvr_constraint_flag is omitted and        inferred to be equal to 1 when intra_only_constraint_flag is        equal to 1.    -   The signalling of no_affine_motion_constraint_flag is omitted        and inferred to be equal to 1 when intra_only_constraint_flag is        equal to 1.    -   The signalling of no_bcw_constraint_flag is omitted and inferred        to be equal to 1 when intra_only_constraint_flag is equal to 1.    -   The signalling of no_ciip_constraint_flag is omitted and        inferred to be equal to 1 when intra_only_constraint_flag is        equal to 1.    -   The signalling of no_fpel_mmvd_constraint_flag is omitted and        inferred to be equal to 1 when intra_only_constraint_flag is        equal to 1.    -   The signalling of no_gpm_constraint_flag is omitted and inferred        to be equal to 1 when intra_only_constraint_flag is equal to 1.

Thus, in some such examples, a device (e.g., source device 102,destination device 116, etc.) may determine that a first syntax elementis omitted from a bitstream and inferred to be equal to 1 based on asecond syntax element indicating there are no chroma components in thebitstream and a third syntax element indicating that all slices of thebitstream are I slices, the first syntax element being one of: ano_qtbtt_dual_tree_intra_constraint_flag, a no_ccalf_constraint_flag, ano_joint_cbcr_constraint_flag, a no_cclm_constraint_flag, ano_ref_wraparound_constraint_flag, a no_temporal_mvp_constraint_flag, ano_sbtmvp_constraint_flag, a no_amvr_constraint_flag, ano_bdof_constraint_flag, a no_dmvr_constraint_flag, ano_affine_motion_constraint_flag, a no_bcw_constraint_flag, ano_ciip_constraint_flag, a no_fpel_mmvd_constraint_flag, or ano_gpm_constraint_flag; and perform a bitstream conformance process thatdetermines whether a bitstream that comprises an encoded representationof the video data conforms to a video coding standard based on the firstsyntax element.

Several coding tools are missing in the general constraint informationsyntax to provide general constraint controls. The missing flags areadded into VVC 8 as shown in Table 3, below:

TABLE 3 Descriptor general_constraint_info( ) { no_mrl_constraint_flagu(1) no_isp_constraint_flag u(1) no_mip_constraint_flag u(1)no_lfnst_constraint_flag u(1) no_mmvd_constraint_flag u(1)no_smvd_constraint_flag u(1) no_prof_constraint_flag u(1)no_palette_constraint_flag u(1) no_act_constraint_flag u(1)no_lmcs_constraint_flag u(1)

Table 4, below, describes semantics of the syntax elements listed inTable 3.

TABLE 4 no_mrl_constraint_flag equal to 1 specifies thatsps_mrl_enabled_flag shall be equal to 0. no_mrl_constraint_flag equalto 0 does not impose such a constraint. no_isp_constraint_flag equal to1 specifies that sps_isp_enabled_flag shall be equal to 0.no_isp_constraint_flag equal to 0 does not impose such a constraint.no_mip_constraint_flag equal to 1 specifies that sps_mip_enabled_flagshall be equal to 0. no_mip_constraint_flag equal to 0 does not imposesuch a constraint. no_lfnst_constraint_flag equal to 1 specifies thatsps_lfnst_enabled_flag shall be equal to 0. no_lfnst_constraint_flagequal to 0 does not impose such a constraint. no_mmvd_constraint_flagequal to 1 specifies that sps_mmvd_enabled_flag shall be equal to 0.no_mmvd_constraint_flag equal to 0 does not impose such a constraint.When intra_only_constraint_flag is equal to 1, the value ofno_mmvd_constraint_flag shall be equal to 1. no_smvd_constraint_flagequal to 1 specifies that sps_smvd_enabled_flag shall be equal to 0.no_smvd_constraint_flag equal to 0 does not impose such a constraint.When intra_only_constraint_flag is equal to 1, the value ofno_smvd_constraint_flag shall be equal to 1. no_prof_constraint_flagequal to 1 specifies that sps_affine_prof_enabled_flag shall be equal to0. no_prof_constraint_flag equal to 0 does not impose such a constraint.When intra_only_constraint_flag is equal to 1, the value ofno_prof_constraint_flag shall be equal to 1. no_palette_constraint_flagequal to 1 specifies that sps_palette_enabled_flag shall be equal to 0.no_palette_constraint_flag equal to 0 does not impose such a constraint.no_act_constraint_flag equal to 1 specifies that sps_act_enabled_flagshall be equal to 0. no_act_constraint_flag equal to 0 does not imposesuch a constraint. no_lmcs_constraint_flag equal to 1 specifies thatsps_lmcs_enabled_flag shall be equal to 0. no_lmcs_constraint_flag equalto 0 does not impose such a constraint.

The semantics of syntax elements mentioned in Table 4, above areprovided in Table 5, below.

TABLE 5 sps_mrl_enabled_flag equal to 1 specifies that intra predictionwith multiple reference lines is enabled. sps_mrl_enabled_flag equal to0 specifies that intra prediction with multiple reference lines isdisabled. sps_isp_enabled_flag equal to 1 specifies that intraprediction with subpartitions is enabled. sps_isp_enabled_flag equal to0 specifies that intra prediction with subpartitions is disabled.sps_mip_enabled_flag equal to 1 specifies that matrix-based intraprediction is enabled. sps_mip_enabled_flag equal to 0 specifies thatmatrix-based intra prediction is disabled. sps_lfnst_enabled_flag equalto 1 specifies that lfnst_idx may be present in intra coding unitsyntax. sps_lfnst_enabled_flag equal to 0 specifies that lfnst_idx isnot present in intra coding unit syntax. lfnst_idx specifies whether andwhich one of the two low frequency non-separable transform kernels in aselected transform set is used. lfnst_idx equal to 0 specifies that thelow frequency non-separable transform is not used in the current codingunit. sps_mmvd_enabled_flag equal to 1 specifies that merge mode withmotion vector difference is enabled. sps_mmvd_enabled_flag equal to 0specifies that merge mode with motion vector difference is disabled.sps_smvd_enabled_flag equal to 1 specifies that symmetric motion vectordifference may be used in motion vector decoding. sps_smvd_enabled_flagequal to 0 specifies that symmetric motion vector difference is not usedin motion vector coding. sps_affine_prof_enabled_flag specifies whetherthe prediction refinement with optical flow can be used for affinemotion compensation. If sps_affine_prof_enabled_flag is equal to 0, theaffine motion compensation shall not be refined with optical flow.Otherwise (sps_affine_prof_enabled_flag is equal to 1), the affinemotion compensation can be refined with optical flow. When not present,the value of sps_affine_prof_enabled_flag is inferred to be equal to 0.sps_palette_enabled_flag equal to 1 specifies that pred_mode_plt_flagmay be present in the coding unit syntax. sps_palette_enabled_flag equalto 0 specifies that pred_mode_plt_flag is not present in the coding unitsyntax. When sps_palette_enabled_flag is not present, it is inferred tobe equal to 0. pred_mode_plt_flag specifies the use of palette mode inthe current coding unit. pred_mode_plt_flag equal to 1 indicates thatpalette mode is applied in the current coding unit. pred_mode_plt_flagequal to 0 indicates that palette mode is not applied in the currentcoding unit. sps_act_enabled_flag equal to 1 specifies that adaptivecolour transform may be used and the cu_act_enabled_flag may be presentin the coding unit syntax. sps_act_enabled_flag equal to 0 speifies thatadaptive colour transform is not used and cu_act_enabled_flag is notpresent in the coding unit syntax. When sps_act_enabled_flag is notpresent, it is inferred to be equal to 0. cu_act_enabled_flag equal to 1specifies that the residuals of the current coding unit are coded inYC_(g)C_(o) colour space. cu_act_enabled_flag equal to 0 specifies thatthe residuals of the current coding unit are coded in original colourspace. When cu_act_enabled_flag is not present, it is inferred to beequal to 0. sps_lmcs_enabled_flag equal to 1 specifies that luma mappingwith chroma scaling is used in the CLVS. sps_lmcs_enabled_flag equal to0 specifies that luma mapping with chroma scaling is not used in theCLVS.

In another example, the flags are conditioned byintra_only_constraint_flag=1 as follows:

-   -   The signalling of no_mmvd_constraint_flag is omitted and        inferred to be equal to 1 when intra_only_constraint_flag is        equal to 1.

The signalling of no_smvd_constraint_flag is omitted and inferred to beequal to 1 when intra_only_constraint_flag is equal to 1.

The signalling of no_prof_constraint_flag is omitted and inferred to beequal to 1 when intra_only_constraint_flag is equal to 1.

Thus, in some examples, a device (e.g., source device 102, destinationdevice 116, etc.) may perform a bitstream conformance process thatdetermines whether a bitstream that comprises an encoded representationof the video data conforms to a video coding standard, wherein thebitstream conformance process determines, based on a first syntaxelement in a sequence parameter set (SPS) indicating that a coding toolis enabled, that the bitstream does not conform to the video codingstandard when a second syntax element of the bitstream indicates thatthe first syntax element shall have a value indicating that the codingtool is not enabled. In such examples, the coding tool may be one of:intra prediction with multiple reference lines, intra prediction withsubpartitions, matrix-based intra prediction, selection of a lowfrequency non-separable transform kernel based on an index, merge modewith motion vector difference, use of symmetric motion vector differencein motion vector decoding, prediction refinement with optical flow foraffine motion compensation, palette prediction mode, adaptive colortransform, or luma mapping with chroma scaling.

In some examples of this disclosure, new general constraint flags areadded into the general constraint information syntax to define thefeatures of single layer and single sublayer. The proposed changes toVVC 8 are shown by the <!> . . . </!> tags as shown in Table 6, below:

TABLE 6 Descriptor general_constraint_info( ) {general_progressive_source_flag u(1) general_interlaced_source_flag u(1)general_non_packed_constraint_flag u(1)general_frame_only_constraint_flag u(1)general_non_projected_constraint_flag u(1) intra_only_constraint_flagu(1) max_bitdepth_constraint_idc u(4) max_chroma_format_constraint_idcu(2)  <!>single_layer_constraint_flag</!> <!>u(1)</!> <!>single_sublayer_constraint_flag</!> <!>u(1)</!> <!>single_sublayer_per_layer_constraint_flag</!> <!>u(1)</!> <!>no_inter_layer_pred_constraint_flag</!> <!>u(1)</!>no_res_change_in_clvs_constraint_flag u(1)one_tile_per_pic_constraint_flag u(1) one_slice_per_pic_constraint_flagu(1) one_subpic_per_pic_constraint_flag u(1)

The semantics of the added syntax elements of Table 6 are presented inTable 7, below:

TABLE 7 <!>single_layer_constraint_flag equal to 1 specifies that it isa requirement of bitstream conformance that sps_video_parameter_set_idshall be equal to 0. single_layer_constraint_flag equal to 0 does notimpose such a constraint.<!> <!>single_sublayer_constraint_flag equal to1 specifies it is a requirement of bitstream conformance that bothsps_video_parameter_set_id and sps_max_sublayers_minus1 shall be equalto 0. single_sublayer_constraint_flag equal to 0 does not impose such aconstraint.</!> <!>single_sublayer_per_layer_constraint_flag equal to 1specifies that it is a requirement of bitstream conformance thatsps_max_sublayers_minus1 shall be equal to 0.single_sublayer_per_layer_constraint_flag equal to 0 does not imposesuch a constraint.</!> <!>no_inter_layer_pred_constraint_flag equal to 1specifies that it is a requirement of bitstream conformance thatvps_all_independent_layers_flag shall be equal to 1.no_inter_layer_pred_constraint_flag equal to 0 does not impose such aconstraint. When single_layer_constraint_flag is equal to 1, the valueof no_inter_layer_pred_constraint_flag shall be equal to 1.</!>

Semantics of syntax elements mentioned in Table 7 are provided in Table8, below.

TABLE 8 sps_video_parameter_set_id, when greater than 0, specifies thevalue of vps_video_parameter_set_id for the VPS referred to by the SPS.When sps_video_parameter_set_id is equal to 0, the following applies: -The SPS does not refer to a VPS. - No VPS is referred to when decodingeach CLVS referring to the SPS. - The value of vps_max_layers_minus1 isinferred to be equal to 0. - The CVS shall contain only one layer (i.e.,all VCL NAL unit in the CVS shall have the same value ofnuh_layer_id). - The value of GeneralLayerIdx[ nuh_layer_id ] isinferred to be equal to 0. - The value of vps_independent_layer_flag[GeneralLayerIdx[ nuh_layer_id ] ] is inferred to be equal to 1. Whenvps_independent_layer_flag[ GeneralLayerIdx[ nuh_layer_id ] ] is equalto 1, the SPS referred to by a CLVS with a particluar nuh_layer_id valuenuhLayerId shall have nuh_layer_id equal to nuhLayerId. The value ofsps_video_parameter_set_id shall be the same in all SPSs that arereferred to by CLVSs in a CVS. sps_max_sublayers_minus1 plus 1 specifiesthe maximum number of temporal sublayers that may be present in eachCLVS referring to the SPS. The value of sps_max_sublayers_minus1 shallbe in the range of 0 to vps_max_sublayers_minus1, inclusive.vps_all_independent_layers_flag equal to 1 specifies that all layers inthe CVS are independently coded without using inter-layer prediction.vps_all_independent_layers_flag equal to 0 specifies that one or more ofthe layers in the CVS may use inter-layer prediction. When not present,the value of vps_all_independent_layers_flag is inferred to be equal to1.

In another example, the flags are conditioned bysingle_layer_constraint_flag as follows:

-   -   The signalling of no_inter_layer_pred_constraint_flag is omitted        and inferred to be equal to 1 when single_layer_constraint_flag        is equal to 1.

Thus, in some such examples, a device (e.g., source device 102,destination device 116, etc.) may perform a bitstream conformanceprocess that determines whether a bitstream that comprises an encodedrepresentation of the video data conforms to a video coding standard. Inthese examples, the bitstream conformance process determines that thebitstream does not conform to the video coding standard based on a firstsyntax element (e.g., single_layer_constraint_flag,single_sublayer_constraint_flag,single_sublayer_per_layer_constraint_flag, orno_inter_layer_pred_constraint_flag) having a particular valueindicating a requirement of bitstream conformance is applicable andbased on the requirement of bitstream conformance not being satisfied.The requirement of bitstream conformance specifies one of: a secondsyntax element (e.g., sps_video_parameter_set_id) specifies a videoparameter set (VPS) identifier of a sequence parameter set (SPS) shallbe equal to 0, the second syntax element shall be equal to 0 and a thirdsyntax element (e.g., sps_max_sublayers_minus1), plus 1, specifies thata maximum number of temporal sublayers that may be present in each codedlayer video sequence (CLVS) shall be equal to 0, the third syntaxelement shall be equal to 0, or a fourth syntax element (e.g.,vps_all_independent_layers_flag) shall specify that all layers in acoded video sequence (CVS) are independently coded without inter-layerprediction.

In some examples of this disclosure, no_vps_constraint_flag andno_ph_constraint_flag are added into the general constraint informationsyntax to define the features of VPS and PH. The proposed changes on topof VVC 8 are shown by the <!> . . . </!> tags as shown in Table 9,below:

TABLE 9 Descriptor general_constraint_info( ) {no_mixed_nalu_types_in_pic_constraint_flag u(1) no_trail_constraint_flagu(1) no_stsa_constraint_flag u(1) no_rasl_constraint_flag u(1)no_radl_constraint_flag u(1) no_idr_constraint_flag u(1)no_cra_constraint_flag u(1) no_gdr_constraint_flag u(1) <!>no_vps_constraint_flag</!> <!>u(1)</!> <!> no_ph_constraint_flag</!><!>u(1)</!> no_aps_constraint_flag u(1)

Semantics of added syntax elements in Table 9 are described in Table 10,below.

TABLE 10 <!>no_vps_constraint_flag equal to 1 specifies that there shallbe no NAL unit with nuh_unit_type equal to VPS_NUT present inOlsInScope. no_vps_constraint_flag equal to 0 does not impose such aconstraint.</!> <!>no_ph_constraint_flag equal to 1 specifies that thereshall be no NAL unit with nuh_unit_type equal to PH_NUT present inOlsInScope. no_ph_constraint_flag equal to 0 does not impose such aconstraint.</!> no_stsa_constraint_flag equal to 1 specifies that thereshall be no NAL unit with nuh_unit_type equal to STSA_NUT present inOlsInScope. no_stsa_constraint_flag equal to 0 does not impose such aconstraint. <!>When single_sublayer_constraint_constraint_flag is equalto 1, the value of no_stsa_constraint_flag shall be equal to 1.</!>

Thus, in this example, a device (e.g., source device 102, destinationdevice 116, etc.) may perform a bitstream conformance process thatdetermines whether a bitstream that comprises an encoded representationof the video data conforms to a video coding standard. In this example,the bitstream conformance process determines that the bitstream does notconform to the video coding standard based on a first syntax element(e.g., no_vps_constraint_flag, no_ph_constraint_flag, etc.) having aparticular value indicating a requirement of bitstream conformance isapplicable and based on the requirement of bitstream conformance notbeing satisfied. The requirement of bitstream conformance specifies oneof: there shall be no Network Abstraction Layer (NAL) unit in thebitstream with a NAL unit type equal to a Video Parameter Set (VPS) NALunit type in an in-scope output layer set, or there shall be no NAL unitin the bitstream with a picture header NAL unit type in the in-scopeoutput layer set.

FIG. 3 is a block diagram illustrating an example video encoder 200.FIG. 3 is provided for purposes of explanation and should not beconsidered limiting of the techniques as broadly exemplified anddescribed in this disclosure. For purposes of explanation, thisdisclosure describes video encoder 200 according to the techniques ofVVC (ITU-T H.266, under development), and HEVC (ITU-T H.265). However,the techniques of this disclosure may be performed by video encodingdevices that are configured to other video coding standards.

In the example of FIG. 3 , video encoder 200 includes video data memory230, mode selection unit 202, residual generation unit 204, transformprocessing unit 206, quantization unit 208, inverse quantization unit210, inverse transform processing unit 212, reconstruction unit 214,filter unit 216, decoded picture buffer (DPB) 218, and entropy encodingunit 220. Any or all of video data memory 230, mode selection unit 202,residual generation unit 204, transform processing unit 206,quantization unit 208, inverse quantization unit 210, inverse transformprocessing unit 212, reconstruction unit 214, filter unit 216, DPB 218,and entropy encoding unit 220 may be implemented in one or moreprocessors or in processing circuitry. For instance, the units of videoencoder 200 may be implemented as one or more circuits or logic elementsas part of hardware circuitry, or as part of a processor, ASIC, of FPGA.Moreover, video encoder 200 may include additional or alternativeprocessors or processing circuitry to perform these and other functions.

Video data memory 230 may store video data to be encoded by thecomponents of video encoder 200. Video encoder 200 may receive the videodata stored in video data memory 230 from, for example, video source 104(FIG. 1 ). DPB 218 may act as a reference picture memory that storesreference video data for use in prediction of subsequent video data byvideo encoder 200. Video data memory 230 and DPB 218 may be formed byany of a variety of memory devices, such as dynamic random access memory(DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. Video datamemory 230 and DPB 218 may be provided by the same memory device orseparate memory devices. In various examples, video data memory 230 maybe on-chip with other components of video encoder 200, as illustrated,or off-chip relative to those components.

In this disclosure, reference to video data memory 230 should not beinterpreted as being limited to memory internal to video encoder 200,unless specifically described as such, or memory external to videoencoder 200, unless specifically described as such. Rather, reference tovideo data memory 230 should be understood as reference memory thatstores video data that video encoder 200 receives for encoding (e.g.,video data for a current block that is to be encoded). Memory 106 ofFIG. 1 may also provide temporary storage of outputs from the variousunits of video encoder 200.

The various units of FIG. 3 are illustrated to assist with understandingthe operations performed by video encoder 200. The units may beimplemented as fixed-function circuits, programmable circuits, or acombination thereof. Fixed-function circuits refer to circuits thatprovide particular functionality, and are preset on the operations thatcan be performed. Programmable circuits refer to circuits that can beprogrammed to perform various tasks, and provide flexible functionalityin the operations that can be performed. For instance, programmablecircuits may execute software or firmware that cause the programmablecircuits to operate in the manner defined by instructions of thesoftware or firmware. Fixed-function circuits may execute softwareinstructions (e.g., to receive parameters or output parameters), but thetypes of operations that the fixed-function circuits perform aregenerally immutable. In some examples, one or more of the units may bedistinct circuit blocks (fixed-function or programmable), and in someexamples, one or more of the units may be integrated circuits.

Video encoder 200 may include arithmetic logic units (ALUs), elementaryfunction units (EFUs), digital circuits, analog circuits, and/orprogrammable cores, formed from programmable circuits. In examples wherethe operations of video encoder 200 are performed using softwareexecuted by the programmable circuits, memory 106 (FIG. 1 ) may storethe instructions (e.g., object code) of the software that video encoder200 receives and executes, or another memory within video encoder 200(not shown) may store such instructions.

Video data memory 230 is configured to store received video data. Videoencoder 200 may retrieve a picture of the video data from video datamemory 230 and provide the video data to residual generation unit 204and mode selection unit 202. Video data in video data memory 230 may beraw video data that is to be encoded.

Mode selection unit 202 includes a motion estimation unit 222, a motioncompensation unit 224, and an intra-prediction unit 226. Mode selectionunit 202 may include additional functional units to perform videoprediction in accordance with other prediction modes. As examples, modeselection unit 202 may include a palette unit, an intra-block copy unit(which may be part of motion estimation unit 222 and/or motioncompensation unit 224), an affine unit, a linear model (LM) unit, or thelike.

Mode selection unit 202 generally coordinates multiple encoding passesto test combinations of encoding parameters and resultingrate-distortion values for such combinations. The encoding parametersmay include partitioning of CTUs into CUs, prediction modes for the CUs,transform types for residual data of the CUs, quantization parametersfor residual data of the CUs, and so on. Mode selection unit 202 mayultimately select the combination of encoding parameters havingrate-distortion values that are better than the other testedcombinations.

Video encoder 200 may partition a picture retrieved from video datamemory 230 into a series of CTUs, and encapsulate one or more CTUswithin a slice. Mode selection unit 202 may partition a CTU of thepicture in accordance with a tree structure, such as the QTBT structureor the quad-tree structure of HEVC described above. As described above,video encoder 200 may form one or more CUs from partitioning a CTUaccording to the tree structure. Such a CU may also be referred togenerally as a “video block” or “block.”

In general, mode selection unit 202 also controls the components thereof(e.g., motion estimation unit 222, motion compensation unit 224, andintra-prediction unit 226) to generate a prediction block for a currentblock (e.g., a current CU, or in HEVC, the overlapping portion of a PUand a TU). For inter-prediction of a current block, motion estimationunit 222 may perform a motion search to identify one or more closelymatching reference blocks in one or more reference pictures (e.g., oneor more previously coded pictures stored in DPB 218). In particular,motion estimation unit 222 may calculate a value representative of howsimilar a potential reference block is to the current block, e.g.,according to sum of absolute difference (SAD), sum of squareddifferences (SSD), mean absolute difference (MAD), mean squareddifferences (MSD), or the like. Motion estimation unit 222 may generallyperform these calculations using sample-by-sample differences betweenthe current block and the reference block being considered. Motionestimation unit 222 may identify a reference block having a lowest valueresulting from these calculations, indicating a reference block thatmost closely matches the current block.

Motion estimation unit 222 may form one or more motion vectors (MVs)that defines the positions of the reference blocks in the referencepictures relative to the position of the current block in a currentpicture. Motion estimation unit 222 may then provide the motion vectorsto motion compensation unit 224. For example, for uni-directionalinter-prediction, motion estimation unit 222 may provide a single motionvector, whereas for bi-directional inter-prediction, motion estimationunit 222 may provide two motion vectors. Motion compensation unit 224may then generate a prediction block using the motion vectors. Forexample, motion compensation unit 224 may retrieve data of the referenceblock using the motion vector. As another example, if the motion vectorhas fractional sample precision, motion compensation unit 224 mayinterpolate values for the prediction block according to one or moreinterpolation filters. Moreover, for bi-directional inter-prediction,motion compensation unit 224 may retrieve data for two reference blocksidentified by respective motion vectors and combine the retrieved data,e.g., through sample-by-sample averaging or weighted averaging.

As another example, for intra-prediction, or intra-prediction coding,intra-prediction unit 226 may generate the prediction block from samplesneighboring the current block. For example, for directional modes,intra-prediction unit 226 may generally mathematically combine values ofneighboring samples and populate these calculated values in the defineddirection across the current block to produce the prediction block. Asanother example, for DC mode, intra-prediction unit 226 may calculate anaverage of the neighboring samples to the current block and generate theprediction block to include this resulting average for each sample ofthe prediction block.

Mode selection unit 202 provides the prediction block to residualgeneration unit 204. Residual generation unit 204 receives a raw,unencoded version of the current block from video data memory 230 andthe prediction block from mode selection unit 202. Residual generationunit 204 calculates sample-by-sample differences between the currentblock and the prediction block. The resulting sample-by-sampledifferences define a residual block for the current block. In someexamples, residual generation unit 204 may also determine differencesbetween sample values in the residual block to generate a residual blockusing residual differential pulse code modulation (RDPCM). In someexamples, residual generation unit 204 may be formed using one or moresubtractor circuits that perform binary subtraction.

In examples where mode selection unit 202 partitions CUs into PUs, eachPU may be associated with a luma prediction unit and correspondingchroma prediction units. Video encoder 200 and video decoder 300 maysupport PUs having various sizes. As indicated above, the size of a CUmay refer to the size of the luma coding block of the CU and the size ofa PU may refer to the size of a luma prediction unit of the PU. Assumingthat the size of a particular CU is 2N×2N, video encoder 200 may supportPU sizes of 2N×2N or N×N for intra prediction, and symmetric PU sizes of2N×2N, 2N×N, N×2N, N×N, or similar for inter prediction. Video encoder200 and video decoder 300 may also support asymmetric partitioning forPU sizes of 2N×nU, 2N×nD, nL×2N, and nR×2N for inter prediction.

In examples where mode selection unit 202 does not further partition aCU into PUs, each CU may be associated with a luma coding block andcorresponding chroma coding blocks. As above, the size of a CU may referto the size of the luma coding block of the CU. The video encoder 200and video decoder 300 may support CU sizes of 2N×2N, 2N×N, or N×2N.

For other video coding techniques such as an intra-block copy modecoding, an affine-mode coding, and linear model (LM) mode coding, as afew examples, mode selection unit 202, via respective units associatedwith the coding techniques, generates a prediction block for the currentblock being encoded. In some examples, such as palette mode coding, modeselection unit 202 may not generate a prediction block, and insteadgenerate syntax elements that indicate the manner in which toreconstruct the block based on a selected palette. In such modes, modeselection unit 202 may provide these syntax elements to entropy encodingunit 220 to be encoded.

As described above, residual generation unit 204 receives the video datafor the current block and the corresponding prediction block. Residualgeneration unit 204 then generates a residual block for the currentblock. To generate the residual block, residual generation unit 204calculates sample-by-sample differences between the prediction block andthe current block.

Transform processing unit 206 applies one or more transforms to theresidual block to generate a block of transform coefficients (referredto herein as a “transform coefficient block”). Transform processing unit206 may apply various transforms to a residual block to form thetransform coefficient block. For example, transform processing unit 206may apply a discrete cosine transform (DCT), a directional transform, aKarhunen-Loeve transform (KLT), or a conceptually similar transform to aresidual block. In some examples, transform processing unit 206 mayperform multiple transforms to a residual block, e.g., a primarytransform and a secondary transform, such as a rotational transform. Insome examples, transform processing unit 206 does not apply transformsto a residual block.

Quantization unit 208 may quantize the transform coefficients in atransform coefficient block, to produce a quantized transformcoefficient block. Quantization unit 208 may quantize transformcoefficients of a transform coefficient block according to aquantization parameter (QP) value associated with the current block.Video encoder 200 (e.g., via mode selection unit 202) may adjust thedegree of quantization applied to the transform coefficient blocksassociated with the current block by adjusting the QP value associatedwith the CU. Quantization may introduce loss of information, and thus,quantized transform coefficients may have lower precision than theoriginal transform coefficients produced by transform processing unit206.

Inverse quantization unit 210 and inverse transform processing unit 212may apply inverse quantization and inverse transforms to a quantizedtransform coefficient block, respectively, to reconstruct a residualblock from the transform coefficient block. Reconstruction unit 214 mayproduce a reconstructed block corresponding to the current block (albeitpotentially with some degree of distortion) based on the reconstructedresidual block and a prediction block generated by mode selection unit202. For example, reconstruction unit 214 may add samples of thereconstructed residual block to corresponding samples from theprediction block generated by mode selection unit 202 to produce thereconstructed block.

Filter unit 216 may perform one or more filter operations onreconstructed blocks. For example, filter unit 216 may performdeblocking operations to reduce blockiness artifacts along edges of CUs.Operations of filter unit 216 may be skipped, in some examples.

Video encoder 200 stores reconstructed blocks in DPB 218. For instance,in examples where operations of filter unit 216 are not needed,reconstruction unit 214 may store reconstructed blocks to DPB 218. Inexamples where operations of filter unit 216 are needed, filter unit 216may store the filtered reconstructed blocks to DPB 218. Motionestimation unit 222 and motion compensation unit 224 may retrieve areference picture from DPB 218, formed from the reconstructed (andpotentially filtered) blocks, to inter-predict blocks of subsequentlyencoded pictures. In addition, intra-prediction unit 226 may usereconstructed blocks in DPB 218 of a current picture to intra-predictother blocks in the current picture.

In general, entropy encoding unit 220 may entropy encode syntax elementsreceived from other functional components of video encoder 200. Forexample, entropy encoding unit 220 may entropy encode quantizedtransform coefficient blocks from quantization unit 208. As anotherexample, entropy encoding unit 220 may entropy encode prediction syntaxelements (e.g., motion information for inter-prediction or intra-modeinformation for intra-prediction) from mode selection unit 202. Entropyencoding unit 220 may perform one or more entropy encoding operations onthe syntax elements, which are another example of video data, togenerate entropy-encoded data. For example, entropy encoding unit 220may perform a context-adaptive variable length coding (CAVLC) operation,a CABAC operation, a variable-to-variable (V2V) length coding operation,a syntax-based context-adaptive binary arithmetic coding (SBAC)operation, a Probability Interval Partitioning Entropy (PIPE) codingoperation, an Exponential-Golomb encoding operation, or another type ofentropy encoding operation on the data. In some examples, entropyencoding unit 220 may operate in bypass mode where syntax elements arenot entropy encoded.

Video encoder 200 may output a bitstream that includes the entropyencoded syntax elements needed to reconstruct blocks of a slice orpicture. In particular, entropy encoding unit 220 may output thebitstream.

The operations described above are described with respect to a block.Such description should be understood as being operations for a lumacoding block and/or chroma coding blocks. As described above, in someexamples, the luma coding block and chroma coding blocks are luma andchroma components of a CU. In some examples, the luma coding block andthe chroma coding blocks are luma and chroma components of a PU.

In some examples, operations performed with respect to a luma codingblock need not be repeated for the chroma coding blocks. As one example,operations to identify a motion vector (MV) and reference picture for aluma coding block need not be repeated for identifying an MV andreference picture for the chroma blocks. Rather, the MV for the lumacoding block may be scaled to determine the MV for the chroma blocks,and the reference picture may be the same. As another example, theintra-prediction process may be the same for the luma coding block andthe chroma coding blocks.

Video encoder 200 represents an example of a device configured to encodevideo data including a memory configured to store video data, and one ormore processing units implemented in circuitry and configured to encodea bitstream. In some examples, video encoder 200 may also perform abitstream conformance process in accordance with any of the examples ofthis disclosure.

FIG. 4 is a block diagram illustrating an example video decoder 300 thatmay perform the techniques of this disclosure. FIG. 4 is provided forpurposes of explanation and is not limiting on the techniques as broadlyexemplified and described in this disclosure. For purposes ofexplanation, this disclosure describes video decoder 300 according tothe techniques of VVC (ITU-T H.266, under development), and HEVC (ITU-TH.265). However, the techniques of this disclosure may be performed byvideo coding devices that are configured to other video codingstandards.

In the example of FIG. 4 , video decoder 300 includes coded picturebuffer (CPB) memory 320, entropy decoding unit 302, predictionprocessing unit 304, inverse quantization unit 306, inverse transformprocessing unit 308, reconstruction unit 310, filter unit 312, anddecoded picture buffer (DPB) 314. Any or all of CPB memory 320, entropydecoding unit 302, prediction processing unit 304, inverse quantizationunit 306, inverse transform processing unit 308, reconstruction unit310, filter unit 312, and DPB 314 may be implemented in one or moreprocessors or in processing circuitry. For instance, the units of videodecoder 300 may be implemented as one or more circuits or logic elementsas part of hardware circuitry, or as part of a processor, ASIC, of FPGA.Moreover, video decoder 300 may include additional or alternativeprocessors or processing circuitry to perform these and other functions.

Prediction processing unit 304 includes motion compensation unit 316 andintra-prediction unit 318. Prediction processing unit 304 may includeadditional units to perform prediction in accordance with otherprediction modes. As examples, prediction processing unit 304 mayinclude a palette unit, an intra-block copy unit (which may form part ofmotion compensation unit 316), an affine unit, a linear model (LM) unit,or the like. In other examples, video decoder 300 may include more,fewer, or different functional components.

CPB memory 320 may store video data, such as an encoded video bitstream,to be decoded by the components of video decoder 300. The video datastored in CPB memory 320 may be obtained, for example, fromcomputer-readable medium 110 (FIG. 1 ). CPB memory 320 may include a CPBthat stores encoded video data (e.g., syntax elements) from an encodedvideo bitstream. Also, CPB memory 320 may store video data other thansyntax elements of a coded picture, such as temporary data representingoutputs from the various units of video decoder 300. DPB 314 generallystores decoded pictures, which video decoder 300 may output and/or useas reference video data when decoding subsequent data or pictures of theencoded video bitstream. CPB memory 320 and DPB 314 may be formed by anyof a variety of memory devices, such as DRAM, including SDRAM, MRAM,RRAM, or other types of memory devices. CPB memory 320 and DPB 314 maybe provided by the same memory device or separate memory devices. Invarious examples, CPB memory 320 may be on-chip with other components ofvideo decoder 300, or off-chip relative to those components.

Additionally or alternatively, in some examples, video decoder 300 mayretrieve coded video data from memory 120 (FIG. 1 ). That is, memory 120may store data as discussed above with CPB memory 320. Likewise, memory120 may store instructions to be executed by video decoder 300, whensome or all of the functionality of video decoder 300 is implemented insoftware to be executed by processing circuitry of video decoder 300.

The various units shown in FIG. 4 are illustrated to assist withunderstanding the operations performed by video decoder 300. The unitsmay be implemented as fixed-function circuits, programmable circuits, ora combination thereof. Similar to FIG. 3 , fixed-function circuits referto circuits that provide particular functionality, and are preset on theoperations that can be performed. Programmable circuits refer tocircuits that can be programmed to perform various tasks, and provideflexible functionality in the operations that can be performed. Forinstance, programmable circuits may execute software or firmware thatcause the programmable circuits to operate in the manner defined byinstructions of the software or firmware. Fixed-function circuits mayexecute software instructions (e.g., to receive parameters or outputparameters), but the types of operations that the fixed-functioncircuits perform are generally immutable. In some examples, one or moreof the units may be distinct circuit blocks (fixed-function orprogrammable), and in some examples, one or more of the units may beintegrated circuits.

Video decoder 300 may include ALUs, EFUs, digital circuits, analogcircuits, and/or programmable cores formed from programmable circuits.In examples where the operations of video decoder 300 are performed bysoftware executing on the programmable circuits, on-chip or off-chipmemory may store instructions (e.g., object code) of the software thatvideo decoder 300 receives and executes.

Entropy decoding unit 302 may receive encoded video data from the CPBand entropy decode the video data to reproduce syntax elements.Prediction processing unit 304, inverse quantization unit 306, inversetransform processing unit 308, reconstruction unit 310, and filter unit312 may generate decoded video data based on the syntax elementsextracted from the bitstream.

In general, video decoder 300 reconstructs a picture on a block-by-blockbasis. Video decoder 300 may perform a reconstruction operation on eachblock individually (where the block currently being reconstructed, i.e.,decoded, may be referred to as a “current block”).

Entropy decoding unit 302 may entropy decode syntax elements definingquantized transform coefficients of a quantized transform coefficientblock, as well as transform information, such as a quantizationparameter (QP) and/or transform mode indication(s). Inverse quantizationunit 306 may use the QP associated with the quantized transformcoefficient block to determine a degree of quantization and, likewise, adegree of inverse quantization for inverse quantization unit 306 toapply. Inverse quantization unit 306 may, for example, perform a bitwiseleft-shift operation to inverse quantize the quantized transformcoefficients. Inverse quantization unit 306 may thereby form a transformcoefficient block including transform coefficients.

After inverse quantization unit 306 forms the transform coefficientblock, inverse transform processing unit 308 may apply one or moreinverse transforms to the transform coefficient block to generate aresidual block associated with the current block. For example, inversetransform processing unit 308 may apply an inverse DCT, an inverseinteger transform, an inverse Karhunen-Loeve transform (KLT), an inverserotational transform, an inverse directional transform, or anotherinverse transform to the transform coefficient block.

Furthermore, prediction processing unit 304 generates a prediction blockaccording to prediction information syntax elements that were entropydecoded by entropy decoding unit 302. For example, if the predictioninformation syntax elements indicate that the current block isinter-predicted, motion compensation unit 316 may generate theprediction block. In this case, the prediction information syntaxelements may indicate a reference picture in DPB 314 from which toretrieve a reference block, as well as a motion vector identifying alocation of the reference block in the reference picture relative to thelocation of the current block in the current picture. Motioncompensation unit 316 may generally perform the inter-prediction processin a manner that is substantially similar to that described with respectto motion compensation unit 224 (FIG. 3 ).

As another example, if the prediction information syntax elementsindicate that the current block is intra-predicted, intra-predictionunit 318 may generate the prediction block according to anintra-prediction mode indicated by the prediction information syntaxelements. Again, intra-prediction unit 318 may generally perform theintra-prediction process in a manner that is substantially similar tothat described with respect to intra-prediction unit 226 (FIG. 3 ).Intra-prediction unit 318 may retrieve data of neighboring samples tothe current block from DPB 314.

Reconstruction unit 310 may reconstruct the current block using theprediction block and the residual block. For example, reconstructionunit 310 may add samples of the residual block to corresponding samplesof the prediction block to reconstruct the current block.

Filter unit 312 may perform one or more filter operations onreconstructed blocks. For example, filter unit 312 may performdeblocking operations to reduce blockiness artifacts along edges of thereconstructed blocks. Operations of filter unit 312 are not necessarilyperformed in all examples.

Video decoder 300 may store the reconstructed blocks in DPB 314. Forinstance, in examples where operations of filter unit 312 are notperformed, reconstruction unit 310 may store reconstructed blocks to DPB314. In examples where operations of filter unit 312 are performed,filter unit 312 may store the filtered reconstructed blocks to DPB 314.As discussed above, DPB 314 may provide reference information, such assamples of a current picture for intra-prediction and previously decodedpictures for subsequent motion compensation, to prediction processingunit 304. Moreover, video decoder 300 may output decoded pictures (e.g.,decoded video) from DPB 314 for subsequent presentation on a displaydevice, such as display device 118 of FIG. 1 .

In this manner, video decoder 300 represents an example of a videodecoding device including a memory configured to store video data, andone or more processing units implemented in circuitry and configured todecode a bitstream. In some examples, video decoder 300 may also performa bitstream conformance process in accordance with any of the examplesof this disclosure.

FIG. 5 is a flowchart illustrating an example method for encoding acurrent block. The current block may comprise a current CU. Althoughdescribed with respect to video encoder 200 (FIGS. 1 and 3 ), it shouldbe understood that other devices may be configured to perform a methodsimilar to that of FIG. 5 .

In this example, video encoder 200 initially predicts the current block(350). For example, video encoder 200 may form a prediction block forthe current block. Video encoder 200 may then calculate a residual blockfor the current block (352). To calculate the residual block, videoencoder 200 may calculate a difference between the original, unencodedblock and the prediction block for the current block. Video encoder 200may then transform the residual block and quantize transformcoefficients of the residual block (354). Next, video encoder 200 mayscan the quantized transform coefficients of the residual block (356).During the scan, or following the scan, video encoder 200 may entropyencode the transform coefficients (358). For example, video encoder 200may encode the transform coefficients using CAVLC or CABAC. Videoencoder 200 may then output the entropy encoded data of the block (360).

FIG. 6 is a flowchart illustrating an example method for decoding acurrent block of video data. The current block may comprise a currentCU. Although described with respect to video decoder 300 (FIGS. 1 and 4), it should be understood that other devices may be configured toperform a method similar to that of FIG. 6 .

Video decoder 300 may receive entropy encoded data for the currentblock, such as entropy encoded prediction information and entropyencoded data for transform coefficients of a residual blockcorresponding to the current block (370). Video decoder 300 may entropydecode the entropy encoded data to determine prediction information forthe current block and to reproduce transform coefficients of theresidual block (372). Video decoder 300 may predict the current block(374), e.g., using an intra- or inter-prediction mode as indicated bythe prediction information for the current block, to calculate aprediction block for the current block. Video decoder 300 may theninverse scan the reproduced transform coefficients (376), to create ablock of quantized transform coefficients. Video decoder 300 may theninverse quantize the transform coefficients and apply an inversetransform to the transform coefficients to produce a residual block(378). Video decoder 300 may ultimately decode the current block bycombining the prediction block and the residual block (380).

FIG. 7 is a flowchart illustrating an example process in accordance withone or more techniques of this disclosure. The process of FIG. 7 may beperformed by a system that includes one or more of source device 102,destination device 116, and/or another device. For instance, someactions of the process may be performed by source device 102, someactions of the process may be performed by destination device 116, andso on. Moreover, in some instances, only some of the actions shown inthe example of FIG. 7 are performed.

In the example of FIG. 7 , the system may obtain a bitstream thatcomprises an encoded representation of video data (400). For instance,in one example, the system (e.g., video encoder 200) may obtain thebitstream by encoding video data. In another example, the system mayreceive the bitstream, e.g., from source device 102. In some examples,the system may store the bitstream on a computer-readable medium (e.g.,memory) and obtain the bitstream from the computer-readable medium.

Furthermore, in the example of FIG. 7 , the system may perform abitstream conformance process that determines whether a bitstream thatcomprises an encoded representation of the video data conforms to avideo coding standard, such as VVC (402). As part of performing thebitstream conformance process, the system may determine that thebitstream does not conform to the video coding standard when at leastone of: a chroma-related constraint flag is equal to 0 and when thereare no chroma components for pictures in the bitstream, or an interprediction-related constraint flag is equal to 0 when all slices of thebitstream are I slices.

Thus, in the example of FIG. 7 , the system may determine whether thechroma-related constraint flag is equal to 0 and there are no chromacomponents for pictures in the bitstream (404). In some examples, thechroma-related constraint flag is a syntax element (e.g.,no_qtbtt_dual_tree_intra_constraint_flag) that indicates whether aquad-tree/binary-tree flag must specify that separate coding treestructures are not used for I slices. In some examples, thechroma-related constraint flag is a syntax element (e.g.,no_ccalf_constraint_flag) that indicates whether a cross-componentadaptive loop filter flag must indicate that a cross-component adaptiveloop filter is disabled. In some examples, the chroma-related constraintflag is a syntax element (e.g., no_joint_cbcr_constraint_flag) thatindicates whether a joint coding of a chroma residuals flag mustindicate that joint coding of chroma residuals is disabled. In someexamples, the chroma-related constraint flag is a syntax element (e.g.,no_cclm_constraint_flag) that indicates whether a cross-component linearmodel intra prediction flag must indicate that cross-component linearmodel intra prediction from a luma component to a chroma component isdisabled.

Additionally, the system may determine whether the interprediction-related constraint flag is equal to 0 and all slices in thebitstream are I slices (406). In some examples, the interprediction-related constraint flag is a syntax element (e.g.,no_ref_wraparound_constraint_flag) that specifies whether a wrap-aroundenabled flag (e.g., sps_rel_wraparound_enabled_flag) must indicate thathorizontal wrap-around motion compensation is not applied in interprediction. In some examples, the inter prediction-related constraintflag is a syntax element (e.g., no_temporal_mvp_constraint_flag) thatspecifies whether a temporal motion vector prediction enabled flag(e.g., sps_temporal_mvp_enabled_flag) must indicate that temporal motionvector predictors are not used in a coded layer video sequence (CLVS).In some examples, the inter prediction-related constraint flag is asyntax element (e.g., no_sbtmvp_constraint_flag) that specifies whethera subblock-based temporal motion vector prediction enabled flag (e.g.,sps_sbtmvp_enabled_flag) must indicate that subblock-based temporalmotion vector predictors are not used in the CLVS. In some examples, theinter prediction-related constraint flag is a syntax element (e.g.,no_amvr_constraint_flag) that specifies whether an adaptive motionvector difference resolution enabled flag (e.g., sps_amvr_enabled_flag)must indicate that adaptive motion vector difference resolution is notused in motion vector coding. In some examples, the interprediction-related constraint flag is a syntax element (e.g.,no_bdof_constraint_flag) that specifies whether a bi-directional opticalflow inter prediction flag (e.g., sps_bdof_enabled_flag) must indicatethat bi-directional optical flow inter prediction is disabled. In someexamples, the inter prediction-related constraint flag is a syntaxelement (e.g., no_dmvr_constraint_flag) that specifies whether a decodermotion vector refinement enabled flag (e.g., sps_dmvr_enabled_flag) mustindicate that decoder motion vector refinement is disabled. In someexamples, the inter prediction-related constraint flag is a syntaxelement (e.g., no_affine_motion_constraint_flag) that specifies whetheran affine enabled flag (e.g., sps_affined_enabled) must indicate that noaffine model based motion compensation is used in the CLVS. In someexamples, the inter prediction-related constraint flag is a syntaxelement (e.g., no_bcw_constraint_flag) that specifies whether abi-prediction with coding unit (CU) weights flag (e.g.,sps_bcw_enabled_flag) must indicate that no bi-prediction with CUweights is used in the CLVS. In some examples, the interprediction-related constraint flag is a syntax element (e.g.,no_ciip_constraint_flag) that specifies whether a combined inter-picturemerge and intra-picture prediction (CIIP) flag (e.g.,sps_ciip_enabled_flag) must indicate that there are no flags thatindicate whether CIIP is applied for a coding unit. In some examples,the inter prediction-related constraint flag is a syntax element (e.g.,no_fpel_mmvd_constraint_flag) that specifies whether a merge mode withmotion vector difference flag (e.g., sps_fpel_mmvd_enabled_flag) mustspecify that merge mode with motion vector difference can use fractionalsample precision. In some examples, the inter prediction-relatedconstraint flag is a syntax element (e.g., no_gpm_constraint_flag) thatspecifies whether a geometric partition based motion compensation flag(e.g., sps_gpm_enabled_flag) must indicate that no geometric partitionbased motion compensation is used in the CLVS.

In some examples, when performing the bitstream conformance process, thedevice may determine that the bitstream does not conform to the videocoding standard based on a first syntax element (e.g.,single_layer_constraint_flag) having a particular value indicating arequirement of bitstream conformance is applicable and based on therequirement of bitstream conformance not being satisfied and therequirement of bitstream conformance specifies a second syntax element(e.g., sps_video_parameter_set_id) specifies a video parameter set (VPS)identifier of a sequence parameter set (SPS) shall be equal to 0.

In some examples, the device may determine that the bitstream does notconform to the video coding standard based on a first syntax element(e.g., single_sublayer_constraint_flag) having a particular value(e.g., 1) indicating a requirement of bitstream conformance isapplicable and the requirement of bitstream conformance specifies asecond syntax element (e.g., sps_video_parameter_set_id) shall be equalto 0 and a third syntax element (e.g., sps_max_sublayers_minus_1), plus1, specifies that a maximum number of temporal sublayers that may bepresent in each coded layer video sequence (CLVS) shall be equal to 0.

In some examples, the device may determine that the bitstream does notconform to the video coding standard based on a first syntax element(e.g., single_sublayer_per_layer_constraint_flag) having a particularvalue (e.g., 1) indicating a requirement of bitstream conformance isapplicable and the requirement of bitstream conformance specifies thatthe third syntax element (e.g., sps_max_sublayers_minus1) shall be equalto 0.

In some examples, the device may determine that the bitstream does notconform to the video coding standard based on a first syntax element(e.g., single_layer_constraint_flag) having a particular valueindicating a requirement of bitstream conformance is applicable and therequirement of bitstream conformance specifies that the fourth syntaxelement (e.g., no_inter_layer_pred_constraint_flag) shall specify thatall layers in the CVS are independently coded without inter-layerprediction. In this example, the device may determine that the firstsyntax element is omitted from the bitstream and is inferred to indicatethat the requirement of bitstream conformance is applicable based on afifth syntax element (e.g., single_layer_constraint_flag) specifyingthat it is a second requirement of bitstream conformance that the VPSidentifier of the SPS shall be equal to 0.

In some examples, the system may determine that the bitstream does notconform to the video coding standard based on a first syntax element(e.g., no_inter_layer_pred_constraint_flag) having a particular value(e.g., 1) indicating a requirement of bitstream conformance isapplicable and the requirement of bitstream conformance specifies afourth syntax element (e.g., no_inter_layer_pred_constraint_flag) shallspecify that all layers in a coded video sequence (CVS) areindependently coded without inter-layer prediction.

In the example of FIG. 7 , the system may determine whether thebitstream conformance process determined that the bitstream conforms tothe video coding standard (408). In response to determining that thebitstream conforms to the video coding standard (“YES” branch of 408),the system may provide the bitstream to video decoder 300 (410). Forinstance, in some examples, the system may output the bitstream tocomputer-readable medium 110 for subsequent receipt by destinationdevice 116. In some examples where the device includes video decoder300, video decoder 300 may decode the bitstream. However, in response todetermining that the bitstream does not conform to the video codingstandard (“NO” branch of 408), the system may reject the bitstream(412). For instance, the system may generate an error message. Thus, inthe example of FIG. 7 , the device may generate an error message basedon a determination that the bitstream does not conform to the videocoding standard, send the bitstream to another device based on adetermination that the bitstream conforms to the video coding standard,or decode the bitstream based on the determination that the bitstreamconforms to the video coding standard.

The following is a non-limiting list of examples in accordance with oneor more techniques of this disclosure.

Aspect 1A: A method of processing video data includes performing abitstream conformance process that determines whether a bitstream thatcomprises an encoded representation of the video data conforms to avideo coding standard, wherein the bitstream conformance process is ableto determine that the bitstream conforms to the video coding standardregardless of a value of a first syntax element when a second syntaxelement indicates that only one slice is allowed per picture, the firstsyntax element indicating whether only one subpicture is allowed persubpicture.

Aspect 2A: A method of processing video data includes performing abitstream conformance process that determines whether a bitstream thatcomprises an encoded representation of the video data conforms to avideo coding standard, wherein the bitstream conformance processdetermines that the bitstream does not conform to the video codingstandard when a chroma-related constraint flag is equal to 0 and whenthere are no chroma components for pictures in the bitstream.

Aspect 3A: The method of aspect 2A, wherein the chroma-relatedconstraint flag is one of: a no_qtbtt_dual_tree_intra_constraint_flag, ano_ccalf_constraint_flag, a no_joint_cbcr_constraint_flag, or ano_cclm_constraint_flag.

Aspect 4A: A method of processing video data includes performing abitstream conformance process that determines whether a bitstream thatcomprises an encoded representation of the video data conforms to avideo coding standard, wherein the bitstream conformance processdetermines that the bitstream does not conform to the video codingstandard when an inter prediction-related constraint flag is equal to 0when all slices of the bitstream are I slices.

Aspect 5A: The method of aspect 4A, wherein the chroma-relatedconstraint flag is one of: a no_ref_wraparound_constraint_flag, ano_temporal_mvp_constraint_flag, a no_sbtmvp_constraint_flag, ano_amvr_constraint_flag, a no_bdof_constraint_flag, ano_dmvr_constraint_flag, a no_affine_motion_constraint_flag, ano_bcw_constraint_flag, a no_ciip_constraint_flag, ano_fpel_mmvd_constraint_flag, or a no_gpm_constraint_flag.

Aspect 6A: A method of processing video data includes determining that afirst syntax element is omitted from a bitstream and inferred to beequal to 1 based on a second syntax element indicating there are nochroma components in the bitstream and a third syntax element indicatingthat all slices of the bitstream are I slices, the first syntax elementbeing one of: a no_qtbtt_dual_tree_intra_constraint_flag, ano_ccalf_constraint_flag, a no_joint_cbcr_constraint_flag, ano_cclm_constraint_flag, a no_ref_wraparound_constraint_flag, ano_temporal_mvp_constraint_flag, a no_sbtmvp_constraint_flag, ano_amvr_constraint_flag, a no_bdof_constraint_flag, ano_dmvr_constraint_flag, a no_affine_motion_constraint_flag, ano_bcw_constraint_flag, a no_ciip_constraint_flag, ano_fpel_mmvd_constraint_flag, or a no_gpm_constraint_flag; andperforming a bitstream conformance process that determines whether abitstream that comprises an encoded representation of the video dataconforms to a video coding standard based on the first syntax element.

Aspect 7A: A method of processing video data includes performing abitstream conformance process that determines whether a bitstream thatcomprises an encoded representation of the video data conforms to avideo coding standard, wherein the bitstream conformance processdetermines, based on a first syntax element in a sequence parameter set(SPS) indicating that a coding tool is enabled, that the bitstream doesnot conform to the video coding standard when a second syntax element ofthe bitstream indicates that the first syntax element shall have a valueindicating that the coding tool is not enabled.

Aspect 8A: The method of aspect 7A, wherein the coding tool is one of:intra prediction with multiple reference lines, intra prediction withsubpartitions, matrix-based intra prediction, selection of a lowfrequency non-separable transform kernel based on an index, merge modewith motion vector difference, use of symmetric motion vector differencein motion vector decoding, prediction refinement with optical flow foraffine motion compensation, palette prediction mode, adaptive colortransform, or luma mapping with chroma scaling.

Aspect 9A: The method of aspect 7A, wherein: the coding tool is one of:merge mode with motion vector difference, use of symmetric motion vectordifference in motion vector decoding, or prediction refinement withoptical flow for affine motion compensation, and the method furthercomprises determining that the second syntax element is omitted from thebitstream and indicates that the first syntax element shall have thevalue indicating that the coding tool is not enabled based on a thirdsyntax element indicating that all slices of the bitstream are I slices.

Aspect 10A: A method of processing video data includes performing abitstream conformance process that determines whether a bitstream thatcomprises an encoded representation of the video data conforms to avideo coding standard, wherein the bitstream conformance processdetermines that the bitstream does not conform to the video codingstandard based on a first syntax element having a particular valueindicating a requirement of bitstream conformance is applicable andbased on the requirement of bitstream conformance not being satisfied,wherein the requirement of bitstream conformance specifies one of: asecond syntax element specifies a video parameter set (VPS) identifierof a sequence parameter set (SPS) shall be equal to 0, the second syntaxelement shall be equal to 0 and a third syntax element, plus 1,specifies that a maximum number of temporal sublayers that may bepresent in each coded layer video sequence (CLVS) shall be equal to 0,the third syntax element shall be equal to 0, or a fourth syntax elementshall specify that all layers in a coded video sequence (CVS) areindependently coded without inter-layer prediction.

Aspect 11A: The method of aspect 10A, wherein: the requirement ofbitstream conformance specifies that the fourth syntax element shallspecify that all layers in the CVS are independently coded withoutinter-layer prediction, and the method further comprises determiningthat the first syntax element is omitted from the bitstream and isinferred to indicate that the requirement of bitstream conformance isapplicable based on a fifth syntax element specifying that it is asecond requirement of bitstream conformance that that VPS identifier ofthe SPS shall be equal to 0.

Aspect 12A: A method of processing video data includes performing abitstream conformance process that determines whether a bitstream thatcomprises an encoded representation of the video data conforms to avideo coding standard, wherein the bitstream conformance processdetermines that the bitstream does not conform to the video codingstandard based on a first syntax element having a particular valueindicating a requirement of bitstream conformance is applicable andbased on the requirement of bitstream conformance not being satisfied,wherein the requirement of bitstream conformance specifies one of: thereshall be no Network Abstraction Layer (NAL) unit in the bitstream with aNAL unit type equal to a Video Parameter Set (VPS) NAL unit type in anin-scope output layer set, or there shall be no NAL unit in thebitstream with a picture header NAL unit type in the in-scope outputlayer set.

Aspect 13A: The method of any of aspects 1A-12A, further comprising atleast one of: generating an error message based on a determination thatthe bitstream does not conform to the video coding standard, sending thebitstream to another device based on a determination that the bitstreamconforms to the video coding standard, or decoding the bitstream basedon the determination that the bitstream conforms to the video codingstandard.

Aspect 14A: A method comprising any combination of aspects 1A-13A.

Aspect 15A: A device for processing video data, the device comprisingone or more means for performing the method of any of aspects 1A-14A.

Aspect 16A: The device of aspect 15A, wherein the one or more meanscomprise one or more processors implemented in circuitry.

Aspect 17A: The device of any of aspects 15A and 16A, further comprisinga memory to store the video data.

Aspect 18A: The device of any of aspects 15A-17A, further comprising adisplay configured to display decoded video data.

Aspect 19A: The device of any of aspects 15A-18A, wherein the devicecomprises one or more of a camera, a computer, a mobile device, abroadcast receiver device, or a set-top box.

Aspect 20A: The device of any of aspects 15A-19A, wherein the devicecomprises a video decoder.

Aspect 21A: The device of any of aspects 15A-20A, wherein the devicecomprises a video encoder.

Aspect 22A: A computer-readable storage medium having stored thereoninstructions that, when executed, cause one or more processors toperform the method of any of aspects 1A-14A.

Aspect 1B: A method of processing video data includes performing abitstream conformance process that determines whether a bitstream thatcomprises an encoded representation of the video data conforms to avideo coding standard, wherein the bitstream conformance processdetermines that the bitstream does not conform to the video codingstandard when at least one of: a chroma-related constraint flag is equalto 0 and when there are no chroma components for pictures in thebitstream, or an inter prediction-related constraint flag is equal to 0when all slices of the bitstream are I slices.

Aspect 2B: The method of aspect 1B, wherein the chroma-relatedconstraint flag is one of: a syntax element that indicates whether aquad-tree/binary-tree flag must specify that separate coding treestructures are not used for I slices, a syntax element that indicateswhether a cross-component adaptive loop filter flag must indicate that across-component adaptive loop filter is disabled, a syntax element thatindicates whether a joint coding of a chroma residuals flag mustindicate that joint coding of chroma residuals is disabled, or a syntaxelement that indicates whether a cross-component linear model intraprediction flag must indicate that cross-component linear model intraprediction from a luma component to a chroma component is disabled.

Aspect 3: The method of any of aspects 1 and 2, wherein the intraprediction-related constraint flag is one of: a syntax element thatspecifies whether a wrap-around enabled flag must indicate thathorizontal wrap-around motion compensation is not applied in interprediction, a syntax element that specifies whether a temporal motionvector prediction enabled flag must indicate that temporal motion vectorpredictors are not used in a coded layer video sequence (CLVS), a syntaxelement that specifies whether a subblock-based temporal motion vectorprediction enabled flag must indicate that subblock-based temporalmotion vector predictors are not used in the CLVS, a syntax element thatspecifies whether an adaptive motion vector difference resolutionenabled flag must indicate that adaptive motion vector differenceresolution is not used in motion vector coding, a syntax element thatspecifies whether a bi-directional optical flow inter prediction flagmust indicate that bi-directional optical flow inter prediction isdisabled, a syntax element that specifies whether a decoder motionvector refinement enabled flag must indicate that decoder motion vectorrefinement is disabled, a syntax element that specifies whether anaffine enabled flag must indicate that no affine model based motioncompensation is used in the CLVS, a syntax element that specifieswhether a bi-prediction with coding unit (CU) weights flag must indicatethat no bi-prediction with CU weights is used in the CLVS, a syntaxelement that specifies whether a combined inter-picture merge andintra-picture prediction (CIIP) flag must indicate that there are noflags that indicate whether CIIP is applied for a coding unit, a syntaxelement that specifies whether a merge mode with motion vectordifference flag must specify that merge mode with motion vectordifference can use fractional sample precision, or a syntax element thatspecifies whether a geometric partition based motion compensation flagmust indicate that no geometric partition based motion compensation isused in the CLVS.

Aspect 4B: The method of any of aspects 1B through 3B, whereinperforming the bitstream conformance process further comprises:determining that the bitstream does not conform to the video codingstandard based on a first syntax element having a particular valueindicating a requirement of bitstream conformance is applicable andbased on the requirement of bitstream conformance not being satisfied,wherein the requirement of bitstream conformance specifies one of: asecond syntax element specifies a video parameter set (VPS) identifierof a sequence parameter set (SPS) shall be equal to 0, the second syntaxelement shall be equal to 0 and a third syntax element, plus 1,specifies that a maximum number of temporal sublayers that may bepresent in each coded layer video sequence (CLVS) shall be equal to 0,the third syntax element shall be equal to 0, or a fourth syntax elementshall specify that all layers in a coded video sequence (CVS) areindependently coded without inter-layer prediction.

Aspect 5B: The method of aspect 4B, wherein: the requirement ofbitstream conformance specifies that the fourth syntax element shallspecify that all layers in the CVS are independently coded withoutinter-layer prediction, and the method further comprises determiningthat the first syntax element is omitted from the bitstream and isinferred to indicate that the requirement of bitstream conformance isapplicable based on a fifth syntax element specifying that it is asecond requirement of bitstream conformance that the VPS identifier ofthe SPS shall be equal to 0.

Aspect 6B: The method of any of aspects 1B through 5B, further includesgenerating an error message based on a determination that the bitstreamdoes not conform to the video coding standard, sending the bitstream toanother device based on a determination that the bitstream conforms tothe video coding standard, or decoding the bitstream based on thedetermination that the bitstream conforms to the video coding standard.

Aspect 7B: A device for processing video data includes a memory to storea bitstream that comprises an encoded representation of the video dataconforms to a video coding standard; and one or more processorsimplemented in circuitry and coupled to the memory, the one or moreprocessors configured to perform a bitstream conformance process thatdetermines whether the bitstream conforms to a video coding standard,wherein the bitstream conformance process determines that the bitstreamdoes not conform to the video coding standard when at least one of: achroma-related constraint flag is equal to 0 and when there are nochroma components for pictures in the bitstream, or an interprediction-related constraint flag is equal to 0 when all slices of thebitstream are I slices.

Aspect 8B: The device of aspect 7B, wherein the chroma-relatedconstraint flag is one of: a syntax element that indicates whether aquad-tree/binary-tree flag must specify that separate coding treestructures are not used for I slices, a syntax element that indicateswhether a cross-component adaptive loop filter flag must indicate that across-component adaptive loop filter is disabled, a syntax element thatindicates whether a joint coding of a chroma residuals flag mustindicate that joint coding of chroma residuals is disabled, or a syntaxelement that indicates whether a cross-component linear model intraprediction flag must indicate that cross-component linear model intraprediction from a luma component to a chroma component is disabled.

Aspect 9B: The device of any of aspects 7B and 8B, wherein the intraprediction-related constraint flag is one of: a syntax element thatspecifies whether a wrap-around enabled flag must indicate thathorizontal wrap-around motion compensation is not applied in interprediction, a syntax element that specifies whether a temporal motionvector prediction enabled flag must indicate that temporal motion vectorpredictors are not used in a coded layer video sequence (CLVS), a syntaxelement that specifies whether a subblock-based temporal motion vectorprediction enabled flag must indicate that subblock-based temporalmotion vector predictors are not used in the CLVS, a syntax element thatspecifies whether an adaptive motion vector difference resolutionenabled flag must indicate that adaptive motion vector differenceresolution is not used in motion vector coding, a syntax element thatspecifies whether a bi-directional optical flow inter prediction flagmust indicate that bi-directional optical flow inter prediction isdisabled, a syntax element that specifies whether a decoder motionvector refinement enabled flag must indicate that decoder motion vectorrefinement is disabled, a syntax element that specifies whether anaffine enabled flag must indicate that no affine model based motioncompensation is used in the CLVS, a syntax element that specifieswhether a bi-prediction with coding unit (CU) weights flag must indicatethat no bi-prediction with CU weights is used in the CLVS, a syntaxelement that specifies whether a combined inter-picture merge andintra-picture prediction (CIIP) flag must indicate that there are noflags that indicate whether CIIP is applied for a coding unit, a syntaxelement that specifies whether a merge mode with motion vectordifference flag must specify that merge mode with motion vectordifference can use fractional sample precision, or a syntax element thatspecifies whether a geometric partition based motion compensation flagmust indicate that no geometric partition based motion compensation isused in the CLVS.

Aspect 10B: The device of any of aspects 7B through 9B, wherein the oneor more processors are configured to, as part performing the bitstreamconformance process: determine that the bitstream does not conform tothe video coding standard based on a first syntax element having aparticular value indicating a requirement of bitstream conformance isapplicable and based on the requirement of bitstream conformance notbeing satisfied, wherein the requirement of bitstream conformancespecifies one of: a second syntax element specifies a video parameterset (VPS) identifier of a sequence parameter set (SPS) shall be equal to0, the second syntax element shall be equal to 0 and a third syntaxelement, plus 1, specifies that a maximum number of temporal sublayersthat may be present in each coded layer video sequence (CLVS) shall beequal to 0, the third syntax element shall be equal to 0, or a fourthsyntax element shall specify that all layers in a coded video sequence(CVS) are independently coded without inter-layer prediction.

Aspect 11B: The device of aspect 10B, wherein: the requirement ofbitstream conformance specifies that the fourth syntax element shallspecify that all layers in the CVS are independently coded withoutinter-layer prediction, and the method further comprises determiningthat the first syntax element is omitted from the bitstream and isinferred to indicate that the requirement of bitstream conformance isapplicable based on a fifth syntax element specifying that it is asecond requirement of bitstream conformance that that VPS identifier ofthe SPS shall be equal to 0.

Aspect 12B: The device of any of aspects 7B through 11B, wherein the oneor more processors are further configured to perform at least one of:generating an error message based on a determination that the bitstreamdoes not conform to the video coding standard, sending the bitstream toanother device based on a determination that the bitstream conforms tothe video coding standard, or decoding the bitstream based on thedetermination that the bitstream conforms to the video coding standard.

Aspect 13B: The device of any of aspects 7B through 12B, wherein thedevice comprises one or more of a camera, a computer, a mobile device, abroadcast receiver device, or a set-top box.

Aspect 14B: A device for processing video data includes means forstoring a bitstream that comprises an encoded representation of thevideo data; and means for performing a bitstream conformance processthat determines whether the bitstream conforms to a video codingstandard, wherein the bitstream conformance process determines that thebitstream does not conform to the video coding standard when at leastone of: a chroma-related constraint flag is equal to 0 and when thereare no chroma components for pictures in the bitstream, or an interprediction-related constraint flag is equal to 0 when all slices of thebitstream are I slices.

Aspect 15B: The device of aspect 14B, wherein the chroma-relatedconstraint flag is one of: a syntax element that indicates whether aquad-tree/binary-tree flag must specify that separate coding treestructures are not used for I slices, a syntax element that indicateswhether a cross-component adaptive loop filter flag must indicate that across-component adaptive loop filter is disabled, a syntax element thatindicates whether a joint coding of a chroma residuals flag mustindicate that joint coding of chroma residuals is disabled, or a syntaxelement that indicates whether a cross-component linear model intraprediction flag must indicate that cross-component linear model intraprediction from a luma component to a chroma component is disabled.

Aspect 16B: The device of any of aspects 14B and 15B, wherein the intraprediction-related constraint flag is one of: a syntax element thatspecifies whether a wrap-around enabled flag must indicate thathorizontal wrap-around motion compensation is not applied in interprediction, a syntax element that specifies whether a temporal motionvector prediction enabled flag must indicate that temporal motion vectorpredictors are not used in a coded layer video sequence (CLVS), a syntaxelement that specifies whether a subblock-based temporal motion vectorprediction enabled flag must indicate that subblock-based temporalmotion vector predictors are not used in the CLVS, a syntax element thatspecifies whether an adaptive motion vector difference resolutionenabled flag must indicate that adaptive motion vector differenceresolution is not used in motion vector coding, a syntax element thatspecifies whether a bi-directional optical flow inter prediction flagmust indicate that bi-directional optical flow inter prediction isdisabled, a syntax element that specifies whether a decoder motionvector refinement enabled flag must indicate that decoder motion vectorrefinement is disabled, a syntax element that specifies whether anaffine enabled flag must indicate that no affine model based motioncompensation is used in the CLVS, a syntax element that specifieswhether a bi-prediction with coding unit (CU) weights flag must indicatethat no bi-prediction with CU weights is used in the CLVS, a syntaxelement that specifies whether a combined inter-picture merge andintra-picture prediction (CIIP) flag must indicate that there are noflags that indicate whether CIIP is applied for a coding unit, a syntaxelement that specifies whether a merge mode with motion vectordifference flag must specify that merge mode with motion vectordifference can use fractional sample precision, or a syntax element thatspecifies whether a geometric partition based motion compensation flagmust indicate that no geometric partition based motion compensation isused in the CLVS.

Aspect 17B: A computer-readable storage medium having stored thereoninstructions that, when executed, cause one or more processors to: storea bitstream that comprises an encoded representation of video data; andperform a bitstream conformance process that determines whether thebitstream conforms to a video coding standard, wherein the bitstreamconformance process determines that the bitstream does not conform tothe video coding standard when at least one of: a chroma-relatedconstraint flag is equal to 0 and when there are no chroma componentsfor pictures in the bitstream, or an inter prediction-related constraintflag is equal to 0 when all slices of the bitstream are I slices.

Aspect 18B: The computer-readable storage medium of aspect 17B, whereinthe chroma-related constraint flag is one of: a syntax element thatindicates whether a quad-tree/binary-tree flag must specify thatseparate coding tree structures are not used for I slices, a syntaxelement that indicates whether a cross-component adaptive loop filterflag must indicate that a cross-component adaptive loop filter isdisabled, a syntax element that indicates whether a joint coding of achroma residuals flag must indicate that joint coding of chromaresiduals is disabled, or a syntax element that indicates whether across-component linear model intra prediction flag must indicate thatcross-component linear model intra prediction from a luma component to achroma component is disabled.

Aspect 19B: The computer-readable storage medium of aspect 18B, whereinthe intra prediction-related constraint flag is one of: a syntax elementthat specifies whether a wrap-around enabled flag must indicate thathorizontal wrap-around motion compensation is not applied in interprediction, a syntax element that specifies whether a temporal motionvector prediction enabled flag must indicate that temporal motion vectorpredictors are not used in a coded layer video sequence (CLVS), a syntaxelement that specifies whether a subblock-based temporal motion vectorprediction enabled flag must indicate that subblock-based temporalmotion vector predictors are not used in the CLVS, a syntax element thatspecifies whether an adaptive motion vector difference resolutionenabled flag must indicate that adaptive motion vector differenceresolution is not used in motion vector coding, a syntax element thatspecifies whether a bi-directional optical flow inter prediction flagmust indicate that bi-directional optical flow inter prediction isdisabled, a syntax element that specifies whether a decoder motionvector refinement enabled flag must indicate that decoder motion vectorrefinement is disabled, a syntax element that specifies whether anaffine enabled flag must indicate that no affine model based motioncompensation is used in the CLVS, a syntax element that specifieswhether a bi-prediction with coding unit (CU) weights flag must indicatethat no bi-prediction with CU weights is used in the CLVS, a syntaxelement that specifies whether a combined inter-picture merge andintra-picture prediction (CIIP) flag must indicate that there are noflags that indicate whether CIIP is applied for a coding unit, a syntaxelement that specifies whether a merge mode with motion vectordifference flag must specify that merge mode with motion vectordifference can use fractional sample precision, or a syntax element thatspecifies whether a geometric partition based motion compensation flagmust indicate that no geometric partition based motion compensation isused in the CLVS.

It is to be recognized that depending on the example, certain acts orevents of any of the techniques described herein can be performed in adifferent sequence, may be added, merged, or left out altogether (e.g.,not all described acts or events are necessary for the practice of thetechniques). Moreover, in certain examples, acts or events may beperformed concurrently, e.g., through multi-threaded processing,interrupt processing, or multiple processors, rather than sequentially.

In this disclosure, references ordinal terms, e.g., first, second, etc.,do not necessary indicate an order, but may merely be used todifferentiate separate items.

In one or more examples, the functions described may be implemented inhardware, software, firmware, or any combination thereof. If implementedin software, the functions may be stored on or transmitted over as oneor more instructions or code on a computer-readable medium and executedby a hardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limitation, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablegate arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the terms “processor” and “processingcircuitry,” as used herein may refer to any of the foregoing structuresor any other structure suitable for implementation of the techniquesdescribed herein. In addition, in some aspects, the functionalitydescribed herein may be provided within dedicated hardware and/orsoftware modules configured for encoding and decoding, or incorporatedin a combined codec. Also, the techniques could be fully implemented inone or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Various examples have been described. These and other examples arewithin the scope of the following claims.

What is claimed is:
 1. A method of processing video data, the methodcomprising: performing a bitstream conformance process that determineswhether a bitstream that comprises an encoded representation of thevideo data conforms to a video coding standard, wherein performing thebitstream conformance process comprises determining that the bitstreamdoes not conform to the video coding standard based on a first syntaxelement having a particular value indicating a requirement of bitstreamconformance is applicable and based on the requirement of bitstreamconformance not being satisfied, and wherein the requirement ofbitstream conformance specifies a second syntax element shall specifythat all layers in a coded video sequence (CVS) are independently codedwithout inter-layer prediction.
 2. The method of claim 1, wherein thebitstream conformance process determines that the bitstream does notconform to the video coding standard when a chroma-related constraintflag is equal to 0 and when there are no chroma components for picturesin the bitstream, wherein the chroma-related constraint flag is one of:a syntax element that indicates whether a quad-tree/binary-tree flagmust specify that separate coding tree structures are not used for Islices, a syntax element that indicates whether a cross-componentadaptive loop filter flag must indicate that a cross-component adaptiveloop filter is disabled, a syntax element that indicates whether a jointcoding of a chroma residuals flag must indicate that joint coding ofchroma residuals is disabled, or a syntax element that indicates whethera cross-component linear model intra prediction flag must indicate thatcross-component linear model intra prediction from a luma component to achroma component is disabled.
 3. The method of claim 1, wherein thebitstream conformance process determines that the bitstream does notconform to the video coding standard when an inter prediction-relatedconstraint flag is equal to 0 and all slices of the bitstream are Islices, wherein the inter prediction-related constraint flag is one of:a syntax element that specifies whether a wrap-around enabled flag mustindicate that horizontal wrap-around motion compensation is not appliedin inter prediction, a syntax element that specifies whether a temporalmotion vector prediction enabled flag must indicate that temporal motionvector predictors are not used in a coded layer video sequence (CLVS), asyntax element that specifies whether a subblock-based temporal motionvector prediction enabled flag must indicate that subblock-basedtemporal motion vector predictors are not used in the CLVS, a syntaxelement that specifies whether an adaptive motion vector differenceresolution enabled flag must indicate that adaptive motion vectordifference resolution is not used in motion vector coding, a syntaxelement that specifies whether a bi-directional optical flow interprediction flag must indicate that bi-directional optical flow interprediction is disabled, a syntax element that specifies whether adecoder motion vector refinement enabled flag must indicate that decodermotion vector refinement is disabled, a syntax element that specifieswhether an affine enabled flag must indicate that no affine model basedmotion compensation is used in the CLVS, a syntax element that specifieswhether a bi-prediction with coding unit (CU) weights flag must indicatethat no bi-prediction with CU weights is used in the CLVS, a syntaxelement that specifies whether a combined inter-picture merge andintra-picture prediction (CIIP) flag must indicate that there are noflags that indicate whether CIIP is applied for a coding unit, a syntaxelement that specifies whether a merge mode with motion vectordifference flag must specify that merge mode with motion vectordifference can use fractional sample precision, or a syntax element thatspecifies whether a geometric partition based motion compensation flagmust indicate that no geometric partition based motion compensation isused in the CLVS.
 4. The method of claim 1, wherein: the requirement ofbitstream conformance specifies that the second syntax element shallspecify that all layers in the CVS are independently coded withoutinter-layer prediction, and the method further comprises determiningthat the first syntax element is omitted from the bitstream and isinferred to indicate that the requirement of bitstream conformance isapplicable based on a third syntax element specifying that it is asecond requirement of bitstream conformance that a VPS identifier of theSPS shall be equal to
 0. 5. The method of claim 1, further comprising atleast one of: generating an error message based on a determination thatthe bitstream does not conform to the video coding standard, sending thebitstream to another device based on a determination that the bitstreamconforms to the video coding standard, or decoding the bitstream basedon the determination that the bitstream conforms to the video codingstandard.
 6. A device for processing video data, the device comprising:a memory to store a bitstream that comprises an encoded representationof the video data conforms to a video coding standard; and one or moreprocessors implemented in circuitry and coupled to the memory, the oneor more processors configured to perform a bitstream conformance processthat determines whether the bitstream conforms to a video codingstandard, wherein the one or more processors are configured to, as partof performing the bitstream conformance process, determine that thebitstream does not conform to the video coding standard based on a firstsyntax element having a particular value indicating a requirement ofbitstream conformance is applicable and based on the requirement ofbitstream conformance not being satisfied, and wherein the requirementof bitstream conformance specifies a second syntax element shall specifythat all layers in a coded video sequence (CVS) are independently codedwithout inter-layer prediction.
 7. The device of claim 6, wherein thebitstream conformance process determines that the bitstream does notconform to the video coding standard when a chroma-related constraintflag is equal to 0 and when there are no chroma components for picturesin the bitstream, wherein the chroma-related constraint flag is one of:a syntax element that indicates whether a quad-tree/binary-tree flagmust specify that separate coding tree structures are not used for Islices, a syntax element that indicates whether a cross-componentadaptive loop filter flag must indicate that a cross-component adaptiveloop filter is disabled, a syntax element that indicates whether a jointcoding of a chroma residuals flag must indicate that joint coding ofchroma residuals is disabled, or a syntax element that indicates whethera cross-component linear model intra prediction flag must indicate thatcross-component linear model intra prediction from a luma component to achroma component is disabled.
 8. The device of claim 6, wherein thebitstream conformance process determines that the bitstream does notconform to the video coding standard when an inter prediction-relatedconstraint flag is equal to 0 and all slices of the bitstream are Islices, wherein the inter prediction-related constraint flag is one of:a syntax element that specifies whether a wrap-around enabled flag mustindicate that horizontal wrap-around motion compensation is not appliedin inter prediction, a syntax element that specifies whether a temporalmotion vector prediction enabled flag must indicate that temporal motionvector predictors are not used in a coded layer video sequence (CLVS), asyntax element that specifies whether a subblock-based temporal motionvector prediction enabled flag must indicate that subblock-basedtemporal motion vector predictors are not used in the CLVS, a syntaxelement that specifies whether an adaptive motion vector differenceresolution enabled flag must indicate that adaptive motion vectordifference resolution is not used in motion vector coding, a syntaxelement that specifies whether a bi-directional optical flow interprediction flag must indicate that bi-directional optical flow interprediction is disabled, a syntax element that specifies whether adecoder motion vector refinement enabled flag must indicate that decodermotion vector refinement is disabled, a syntax element that specifieswhether an affine enabled flag must indicate that no affine model basedmotion compensation is used in the CLVS, a syntax element that specifieswhether a bi-prediction with coding unit (CU) weights flag must indicatethat no bi-prediction with CU weights is used in the CLVS, a syntaxelement that specifies whether a combined inter-picture merge andintra-picture prediction (CIIP) flag must indicate that there are noflags that indicate whether CIIP is applied for a coding unit, a syntaxelement that specifies whether a merge mode with motion vectordifference flag must specify that merge mode with motion vectordifference can use fractional sample precision, or a syntax element thatspecifies whether a geometric partition based motion compensation flagmust indicate that no geometric partition based motion compensation isused in the CLVS.
 9. The device of claim 6, wherein: the requirement ofbitstream conformance specifies that the second syntax element shallspecify that all layers in the CVS are independently coded withoutinter-layer prediction, and the method further comprises determiningthat the first syntax element is omitted from the bitstream and isinferred to indicate that the requirement of bitstream conformance isapplicable based on a third syntax element specifying that it is asecond requirement of bitstream conformance that a VPS identifier of theSPS shall be equal to
 0. 10. The device of claim 6, wherein the one ormore processors are further configured to perform at least one of:generating an error message based on a determination that the bitstreamdoes not conform to the video coding standard, sending the bitstream toanother device based on a determination that the bitstream conforms tothe video coding standard, or decoding the bitstream based on thedetermination that the bitstream conforms to the video coding standard.11. The device of claim 6, wherein the device comprises one or more of acamera, a computer, a mobile device, a broadcast receiver device, or aset-top box.
 12. A device for processing video data, the devicecomprising: means for storing a bitstream that comprises an encodedrepresentation of the video data; and means for performing a bitstreamconformance process that determines whether the bitstream conforms to avideo coding standard, wherein the bitstream conformance processdetermines that the bitstream does not conform to the video codingstandard based on a first syntax element having a particular valueindicating a requirement of bitstream conformance is applicable andbased on the requirement of bitstream conformance not being satisfied,and wherein the requirement of bitstream conformance specifies a secondsyntax element shall specify that all layers in a coded video sequence(CVS) are independently coded without inter-layer prediction.
 13. Thedevice of claim 12, wherein the bitstream conformance process determinesthat the bitstream does not conform to the video coding standard when achroma-related constraint flag is equal to 0 and when there are nochroma components for pictures in the bitstream, wherein thechroma-related constraint flag is one of: a syntax element thatindicates whether a quad-tree/binary-tree flag must specify thatseparate coding tree structures are not used for I slices, a syntaxelement that indicates whether a cross-component adaptive loop filterflag must indicate that a cross-component adaptive loop filter isdisabled, a syntax element that indicates whether a joint coding of achroma residuals flag must indicate that joint coding of chromaresiduals is disabled, or a syntax element that indicates whether across-component linear model intra prediction flag must indicate thatcross-component linear model intra prediction from a luma component to achroma component is disabled.
 14. The device of claim 12, wherein thebitstream conformance process determines that the bitstream does notconform to the video coding standard when an inter prediction-relatedconstraint flag is equal to 0 and all slices of the bitstream are Islices, wherein the inter prediction-related constraint flag is one of:a syntax element that specifies whether a wrap-around enabled flag mustindicate that horizontal wrap-around motion compensation is not appliedin inter prediction, a syntax element that specifies whether a temporalmotion vector prediction enabled flag must indicate that temporal motionvector predictors are not used in a coded layer video sequence (CLVS), asyntax element that specifies whether a subblock-based temporal motionvector prediction enabled flag must indicate that subblock-basedtemporal motion vector predictors are not used in the CLVS, a syntaxelement that specifies whether an adaptive motion vector differenceresolution enabled flag must indicate that adaptive motion vectordifference resolution is not used in motion vector coding, a syntaxelement that specifies whether a bi-directional optical flow interprediction flag must indicate that bi-directional optical flow interprediction is disabled, a syntax element that specifies whether adecoder motion vector refinement enabled flag must indicate that decodermotion vector refinement is disabled, a syntax element that specifieswhether an affine enabled flag must indicate that no affine model basedmotion compensation is used in the CLVS, a syntax element that specifieswhether a bi-prediction with coding unit (CU) weights flag must indicatethat no bi-prediction with CU weights is used in the CLVS, a syntaxelement that specifies whether a combined inter-picture merge andintra-picture prediction (CIIP) flag must indicate that there are noflags that indicate whether CIIP is applied for a coding unit, a syntaxelement that specifies whether a merge mode with motion vectordifference flag must specify that merge mode with motion vectordifference can use fractional sample precision, or a syntax element thatspecifies whether a geometric partition based motion compensation flagmust indicate that no geometric partition based motion compensation isused in the CLVS.
 15. A non-transitory computer-readable storage mediumhaving stored thereon instructions that, when executed, cause one ormore processors to: store a bitstream that comprises an encodedrepresentation of video data; and perform a bitstream conformanceprocess that determines whether the bitstream conforms to a video codingstandard, wherein the bitstream conformance process determines that thebitstream does not conform to the video coding standard based on a firstsyntax element having a particular value indicating a requirement ofbitstream conformance is applicable and based on the requirement ofbitstream conformance not being satisfied, and wherein the requirementof bitstream conformance specifies a second syntax element shall specifythat all layers in a coded video sequence (CVS) are independently codedwithout inter-layer prediction.
 16. The non-transitory computer-readablestorage medium of claim 15, wherein the bitstream conformance processdetermines that the bitstream does not conform to the video codingstandard when a chroma-related constraint flag is equal to 0 and whenthere are no chroma components for pictures in the bitstream, whereinthe chroma-related constraint flag is one of: a syntax element thatindicates whether a quad-tree/binary-tree flag must specify thatseparate coding tree structures are not used for I slices, a syntaxelement that indicates whether a cross-component adaptive loop filterflag must indicate that a cross-component adaptive loop filter isdisabled, a syntax element that indicates whether a joint coding of achroma residuals flag must indicate that joint coding of chromaresiduals is disabled, or a syntax element that indicates whether across-component linear model intra prediction flag must indicate thatcross-component linear model intra prediction from a luma component to achroma component is disabled.
 17. The non-transitory computer-readablestorage medium of claim 16, wherein the bitstream conformance processdetermines that the bitstream does not conform to the video codingstandard when an inter prediction-related constraint flag is equal to 0and all slices of the bitstream are I slices, wherein the interprediction-related constraint flag is one of: a syntax element thatspecifies whether a wrap-around enabled flag must indicate thathorizontal wrap-around motion compensation is not applied in interprediction, a syntax element that specifies whether a temporal motionvector prediction enabled flag must indicate that temporal motion vectorpredictors are not used in a coded layer video sequence (CLVS), a syntaxelement that specifies whether a subblock-based temporal motion vectorprediction enabled flag must indicate that subblock-based temporalmotion vector predictors are not used in the CLVS, a syntax element thatspecifies whether an adaptive motion vector difference resolutionenabled flag must indicate that adaptive motion vector differenceresolution is not used in motion vector coding, a syntax element thatspecifies whether a bi-directional optical flow inter prediction flagmust indicate that bi-directional optical flow inter prediction isdisabled, a syntax element that specifies whether a decoder motionvector refinement enabled flag must indicate that decoder motion vectorrefinement is disabled, a syntax element that specifies whether anaffine enabled flag must indicate that no affine model based motioncompensation is used in the CLVS, a syntax element that specifieswhether a bi-prediction with coding unit (CU) weights flag must indicatethat no bi-prediction with CU weights is used in the CLVS, a syntaxelement that specifies whether a combined inter-picture merge andintra-picture prediction (CIIP) flag must indicate that there are noflags that indicate whether CIIP is applied for a coding unit, a syntaxelement that specifies whether a merge mode with motion vectordifference flag must specify that merge mode with motion vectordifference can use fractional sample precision, or a syntax element thatspecifies whether a geometric partition based motion compensation flagmust indicate that no geometric partition based motion compensation isused in the CLVS.